Methods and circuitry for built-in self-testing of circuitry and/or transducers in ultrasound devices

ABSTRACT

Aspects of the technology described herein relate to built-in self-testing (BIST) of circuitry (e.g., a pulser or receive circuitry) and/or transducers in an ultrasound device. A BIST circuit may include a transconductance amplifier coupled between a pulser and receive circuitry, a capacitor network coupled between a pulser and receive circuitry, and/or a current source couplable to the input terminal of receive circuitry to which a transducer is also couplable. The collapse voltages of transducers may be characterized using BIST circuitry, and a bias voltage may be applied to the membranes of the transducers based at least in part on their collapse voltages. The capacitances of transducers may also be measured using BIST circuitry and a notification may be generated based on the sets of measurements.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. § 119(e) ofU.S. Patent Application Ser. No. 63/011,214, filed Apr. 16, 2020, andentitled “METHODS AND CIRCUITRY FOR BUILT-IN SELF-TESTING OF CIRCUITRYAND/OR TRANSDUCERS IN ULTRASOUND DEVICES,” which is hereby incorporatedby reference herein in its entirety.

The present application claims the benefit under 35 U.S.C. § 119(e) ofU.S. Patent Application Ser. No. 63/046,624, filed Jun. 30, 2020, andentitled “METHODS AND CIRCUITRY FOR BUILT-IN SELF-TESTING OF CIRCUITRYAND/OR TRANSDUCERS IN ULTRASOUND DEVICES,” which is hereby incorporatedby reference herein in its entirety.

The present application claims the benefit under 35 U.S.C. § 119(e) ofU.S. Patent Application Ser. No. 63/087,558, filed Oct. 5, 2020, andentitled “METHODS AND CIRCUITRY FOR BUILT-IN SELF-TESTING OF CIRCUITRYAND/OR TRANSDUCERS IN ULTRASOUND DEVICES,” which is hereby incorporatedby reference herein in its entirety.

FIELD

Generally, the aspects of the technology described herein relate toultrasound devices. Some aspects relate to methods and circuitry forbuilt-in self-testing of circuitry and/or transducers in ultrasounddevices.

BACKGROUND

Ultrasound probes may be used to perform diagnostic imaging and/ortreatment, using sound waves with frequencies that are higher than thoseaudible to humans. Ultrasound imaging may be used to see internal softtissue body structures. When pulses of ultrasound are transmitted intotissue, sound waves of different amplitudes may be reflected backtowards the probe at different tissue interfaces. These reflected soundwaves may then be recorded and displayed as an image to the operator.The strength (amplitude) of the sound signal and the time it takes forthe wave to travel through the body may provide information used toproduce the ultrasound image. Many different types of images can beformed using ultrasound devices. For example, images can be generatedthat show two-dimensional cross-sections of tissue, blood flow, motionof tissue over time, the location of blood, the presence of specificmolecules, the stiffness of tissue, or the anatomy of athree-dimensional region.

SUMMARY

According to one aspect of the application, an ultrasound devicecomprises a pulser, receive circuitry, a capacitive micromachinedultrasonic transducer (CMUT) couplable to the receive circuitry, and atransconductance amplifier coupled between the pulser and the receivecircuitry.

In some embodiments, the transconductance amplifier includes alinearized transconductance amplifier. In some embodiments, thetransconductance amplifier includes a source-degenerated linearizedtransconductance amplifier. In some embodiments, the ultrasound devicefurther includes a resistor ladder, and the transconductance amplifierand the pulser are configured to receive, as input signals, voltagesfrom the resistor ladder. In some embodiments, the transconductanceamplifier is coupled between the pulser and a circuit in the receivecircuitry configurable as a transimpedance amplifier. In someembodiments, the transconductance amplifier is coupled between thepulser and a circuit in the receive circuitry configurable as acomparator. In some embodiments, the transconductance amplifier iscoupled between the pulser and a circuit in the receive circuitryconfigurable as a delta-sigma analog-to-digital converter. In someembodiments, the pulser is configured to use a first power supply, thetransconductance amplifier is configured to use a second power supply,the receive circuitry is configured to use a third power supply, and thefirst power supply has a higher voltage than the second power supply andthe second power supply has a higher voltage than the third powersupply. In some embodiments, the transconductance amplifier can beturned off while the pulser and the receive circuitry remain on. In someembodiments, the pulser, the receive circuitry, the CMUT, and thetransconductance amplifier are disposed within a single package. In someembodiments, the transconductance amplifier is disposed on a samesemiconductor chip as the pulser, the receive circuitry, and/or theCMUT. In some embodiments, the transconductance amplifier includes abuilt-in self-test (BIST) circuit.

According to another aspect of the application, an ultrasound deviceincludes receive circuitry having an input terminal, a capacitivemicromachined ultrasonic transducer (CMUT) couplable to the inputterminal of the receive circuitry, and a current source couplable to theinput terminal of the receive circuitry.

In some embodiments, the current source includes a first current sourceconfigured to supply current to the input terminal of the receivecircuitry, and the ultrasound device further includes a second currentsource couplable to the input terminal of the receive circuitry andconfigured to sink current from the input terminal of the receivecircuitry. In some embodiments, the receive circuitry is capable ofbeing configured as a comparator. In some embodiments, the pulser, thereceive circuitry, the CMUT, and the current source are disposed withina single package. In some embodiments, the current source is disposed ona same semiconductor chip as the pulser, the receive circuitry, and/orthe CMUT. In some embodiments, the current source includes a built-inself-test (BIST) circuit.

According to another aspect of the application, an ultrasound deviceincludes a pulser, receive circuitry, and a capacitor network coupledbetween the pulser and the receive circuitry.

In some embodiments, the capacitor network is coupled between the pulserand a circuit in the receive circuitry capable of being configured as aunity-gain amplifier. In some embodiments, the capacitor network isconfigured to attenuate an output signal from the pulser. In someembodiments, the capacitor network is configured to receive, as an inputsignal, an output signal from the pulser, and to output an attenuatedversion of the output signal from the pulser to the pulser and thereceive circuitry. In some embodiments, the pulser, the receivecircuitry, and the capacitor network are disposed within a singlepackage. In some embodiments, the capacitor network is disposed on asame semiconductor chip as the pulser and/or the receive circuitry. Insome embodiments, the capacitor network includes a built-in self-test(BIST) circuit.

According to another aspect of the application, an ultrasound deviceincludes a pulser, a transconductance amplifier, and receive circuitry,and a method for testing the pulser in the ultrasound device includesconverting a voltage output by the pulser to a current using thetransconductance amplifier and outputting the current from thetransconductance amplifier to the receive circuitry.

In some embodiments, the transconductance amplifier includes alinearized transconductance amplifier. In some embodiments, thetransconductance amplifier includes a source-degenerated linearizedtransconductance amplifier. In some embodiments, the transconductanceamplifier and the pulser receive, as input signals, voltages from aresistor ladder. In some embodiments, outputting the current from thetransconductance amplifier to the receive circuitry includes outputtingthe current to a transimpedance amplifier in the receive circuitry. Insome embodiments, outputting the current from the transconductanceamplifier to the receive circuitry includes outputting the current to adelta-sigma analog-to-digital converter in the receive circuitry. Insome embodiments, the pulser uses a first power supply, thetransconductance amplifier uses a second power supply, the receivecircuitry uses a third power supply, and the first power supply has ahigher voltage than the second power supply and the second power supplyhas a higher voltage than the third power supply. In some embodiments,the method further includes turning off the transconductance amplifierwhile the pulser and the receive circuitry remain on. In someembodiments, the pulser, the receive circuitry, a capacitivemicromachined ultrasonic transducer (CMUT), and the transconductanceamplifier are disposed within a single package. In some embodiments, thetransconductance amplifier is disposed on a same semiconductor chip asthe pulser, the receive circuitry, and/or a capacitive micromachinedultrasonic transducer (CMUT). In some embodiments, the transconductanceamplifier includes a built-in self-test (BIST) circuit.

According to another aspect of the application, a method forcharacterizing a capacitive micromachined ultrasonic transducer (CMUT)in an ultrasound device includes generating a current using atransconductance amplifier of the ultrasound device and injecting thecurrent to an input terminal of receive circuitry in the ultrasounddevice, where the input terminal of the receive circuitry iselectrically coupled to the CMUT.

In some embodiments, generating the current includes generating aconstant current. In some embodiments, the transconductance amplifierincludes a linearized transconductance amplifier. In some embodiments,the transconductance amplifier includes a source-degenerated linearizedtransconductance amplifier. In some embodiments, injecting the currentto the input terminal of the receive circuitry includes injecting thecurrent to an input terminal of a comparator in the receive circuitry.In some embodiments, the current charges or discharges the CMUT togenerate a ramp voltage, and the method further includes measuring atime it takes for the ramp voltage to cross a reference voltage. In someembodiments, the method further includes applying a first bias voltageto the CMUT and the current charges or discharges the CMUT to generate afirst ramp voltage when the first bias voltage is applied to the CMUT,measuring a first time it takes for the first ramp voltage to cross areference voltage applying a second bias voltage to the CMUT and thecurrent charges or discharges the CMUT to generate a second ramp voltagewhen the second bias voltage is applied to the CMUT, and measuring asecond time it takes for the second ramp voltage to cross the referencevoltage. In some embodiments, the first bias voltage is applied beforethe second bias voltage, and the first bias voltage is smaller than thesecond bias voltage. In some embodiments, the method further includestransmitting measurements of the first time and the second time to aprocessing device in operative communication with the ultrasound device.In some embodiments, the receive circuitry, the CMUT, and thetransconductance amplifier are disposed within a single package. In someembodiments, the transconductance amplifier is disposed on a samesemiconductor chip as the receive circuitry, and/or the CMUT. In someembodiments, the transconductance amplifier includes a built-inself-test (BIST) circuit.

According to another aspect of the application, a method for testingcircuitry of an ultrasound device includes converting a voltageoutputted by a pulser in the ultrasound device to a first current usinga transconductance amplifier, outputting the first current to receivecircuitry in the ultrasound device, generating a second current usingthe transconductance amplifier, and injecting the second current to aninput terminal of the receive circuitry in the ultrasound device, wherethe input terminal of the receive circuitry is electrically coupled to acapacitive micromachined ultrasonic transducer (CMUT) of the ultrasounddevice.

In some embodiments, the transconductance amplifier includes alinearized transconductance amplifier. In some embodiments, thetransconductance amplifier includes a source-degenerated linearizedtransconductance amplifier. In some embodiments, the transconductanceamplifier and the pulser receive, as input signals, voltages from aresistor ladder. In some embodiments, outputting the first current tothe receive circuitry includes outputting the first current to atransimpedance amplifier in the receive circuitry. In some embodiments,outputting the first current to the receive circuitry includesoutputting the first current to a delta-sigma analog-to-digitalconverter in the receive circuitry. In some embodiments, generating thesecond current includes generating a constant current. In someembodiments, injecting the second current to the input terminal of thereceive circuitry includes injecting the second current to an inputterminal of a comparator in the receive circuitry. In some embodiments,the second current is integrated onto the CMUT to generate a rampvoltage, and the method further includes measuring a time it takes forthe ramp voltage to cross a reference voltage. In some embodiments, themethod further includes applying a first bias voltage to the CMUT andthe second current is integrated onto the CMUT to generate a first rampvoltage when the first bias voltage is applied to the CMUT, measuring afirst time it takes for the first ramp voltage to cross a referencevoltage, applying a second bias voltage to the CMUT and the secondcurrent is integrated onto the CMUT to generate a second ramp voltagewhen the second bias voltage is applied to the CMUT, and measuring asecond time it takes for the second ramp voltage to cross the referencevoltage. In some embodiments, the first bias voltage is applied beforethe second bias voltage, and the first bias voltage is smaller than thesecond bias voltage. In some embodiments, the method further includestransmitting measurements of the first time and the second time to aprocessing device in operative communication with the ultrasound device.In some embodiments, the pulser uses a first power supply, thetransconductance amplifier uses a second power supply, the receivecircuitry uses a third power supply, and the first power supply has ahigher voltage than the second power supply and the second power supplyhas a higher voltage than the third power supply. In some embodiments,the method further includes turning off the transconductance amplifierwhile the pulser and the receive circuitry remain on. In someembodiments, the pulser, the receive circuitry, the CMUT, and thetransconductance amplifier are disposed within a single package. In someembodiments, the transconductance amplifier is disposed on a samesemiconductor chip as the pulser, the receive circuitry, and/or theCMUT. In some embodiments, the transconductance amplifier includes abuilt-in self-test (BIST) circuit.

According to another aspect of the application, a method forcharacterizing a capacitive micromachined ultrasonic transducer (CMUT)in an ultrasound device includes operating a current source in theultrasound device to inject a current to an input terminal of receivecircuitry in the ultrasound device, where the input terminal iselectrically coupled to the CMUT.

In some embodiments, injecting the current to the input terminal of thereceive circuitry includes injecting the current to the input terminalof a comparator in the receive circuitry. In some embodiments, thecurrent charges or discharges the CMUT to generate a ramp voltage, andthe method further includes measuring a time it takes for the rampvoltage to cross a reference voltage. In some embodiments, injecting thecurrent to the input terminal of the receive circuitry includes sourcinga first current to the input terminal of the receive circuitry, wherethe first current charges the CMUT to generate a first ramp voltage, andthe method further includes measuring a first time it takes for thefirst ramp voltage to cross a reference voltage, sinking a secondcurrent from the input terminal of the receive circuitry, where thesecond current discharges the CMUT to generate a second ramp voltage,and measuring a second time it takes for the second ramp voltage tocross the reference voltage. In some embodiments, the method furtherincludes applying a first bias voltage to the CMUT and the current isintegrated onto the CMUT to generate a first ramp voltage when the firstbias voltage is applied to the CMUT, measuring a first time it takes forthe first ramp voltage to cross a reference voltage, applying a secondbias voltage to the CMUT and the current is integrated onto the CMUT togenerate a second ramp voltage when the second bias voltage is appliedto the CMUT, and measuring a second time it takes for the second rampvoltage to cross the reference voltage. In some embodiments, the firstbias voltage is applied before the second bias voltage, and the firstbias voltage is smaller than the second bias voltage. In someembodiments, the method further includes transmitting measurements ofthe first time and the second time to a processing device in operativecommunication with the ultrasound device. In some embodiments, thereceive circuitry, the CMUT, and the current source are disposed withina single package. In some embodiments, the current source is disposed ona same semiconductor chip as the receive circuitry and/or the CMUT. Insome embodiments, the current source includes a built-in self-test(BIST) circuit.

According to another aspect of the application, a method for testing apulser in an ultrasound device includes attenuating a voltage outputtedby the pulser using a capacitor network in the ultrasound device andoutputting the attenuated voltage from the capacitor network to receivecircuitry in the ultrasound device.

In some embodiments, outputting the attenuated voltage to the receivecircuitry includes outputting the attenuated voltage to a unity-gainamplifier in the receive circuitry. In some embodiments, the methodfurther includes providing a feedback voltage to the pulser. In someembodiments, the feedback voltage is attenuated relative to the voltageoutputted by the pulser. In some embodiments, the pulser, the receivecircuitry, and the capacitor network are disposed within a singlepackage. In some embodiments, the capacitor network is disposed on asame semiconductor chip as the pulser and/or the receive circuitry. Insome embodiments, the capacitor network includes a built-in self-test(BIST) circuit.

According to another aspect of the application, a method for testingreceive circuitry in an ultrasound device, includes converting a voltageoutputted by the pulser to a current using a transconductance amplifierin the ultrasound device and outputting the current from thetransconductance amplifier to the receive circuitry in the ultrasounddevice.

In some embodiments, the transconductance amplifier includes alinearized transconductance amplifier. In some embodiments, thetransconductance amplifier includes a source-degenerated linearizedtransconductance amplifier. In some embodiments, the pulser, the receivecircuitry, and the transconductance amplifier are disposed within asingle package. In some embodiments, the transconductance amplifier isdisposed on a same semiconductor chip as the pulser and/or the receivecircuitry. In some embodiments, the transconductance amplifier includesa built-in self-test (BIST) circuit.

According to another aspect of the application, an apparatus includes aprocessing device in operative communication with an ultrasound device,the processing device configured to: receive, from the ultrasound devicesets of measurements of capacitances or a parameter related to thecapacitances of one or more CMUTs in the ultrasound device at each ofmultiple bias voltages applied to the membranes of the CMUTs; determinecollapse voltages of the one or more CMUTs based on the capacitances ofthe CMUTs at each of the multiple bias voltages; and cause theultrasound device to apply a bias voltage to the membranes of the CMUTsbased at least in part on the collapse voltages of the one or moreCMUTs.

In some embodiments, each of the measurements of the parameter relatedto the capacitances of the one or more CMUTs in the ultrasound deviceincludes a measurement of a time for a ramp voltage to cross a referencevoltage, and where a current is integrated onto one of the CMUTs togenerate the ramp voltage when a particular bias voltage of the multiplebias voltages is applied to the CMUT. In some embodiments, theprocessing device is further configured to compute the capacitances ofthe one or more CMUTs in the ultrasound device based on the measurementsof the parameter related to the capacitances of the one or more CMUTs inthe ultrasound device. In some embodiments, the processing device isconfigured, when determining the collapse voltages of the one or moreCMUTs based on the capacitances of the one or more CMUTs at each of themultiple bias voltages, to determine a particular bias voltage at whicha discontinuity occurs in a curve of capacitance versus bias voltage foreach of the one or more CMUTs. In some embodiments, the processingdevice is further configured to average the collapse voltages of the oneor more CMUTs to produce an average of the collapse voltages. In someembodiments, the processing device is configured, when causing theultrasound device to apply the bias voltage to the membranes of the oneor more CMUTs based at least in part on the collapse voltages of the oneor more CMUTs, to cause the ultrasound device to apply a bias voltage tothe membranes of the one or more CMUTs that is greater than the averageof the collapse voltages by an offset voltage. In some embodiments, themembranes of the one or more CMUTs include one shared membrane. In someembodiments, the offset voltage is approximately equal to or between25-30V. In some embodiments, the processing device is further configuredto use different offset voltages when the ultrasound device is imagingdifferent anatomical regions.

According to another aspect of the application, a method includes:receiving, by a processing device in operative communication with anultrasound device and from the ultrasound device, sets of measurementsof capacitances or a parameter related to the capacitances of one ormore CMUTs in the ultrasound device at each of multiple bias voltagesapplied to the membranes of the one or more CMUTs; determining collapsevoltages of the one or more CMUTs based on the capacitances of the oneor more CMUTs at each of the multiple bias voltages; and causing theultrasound device to apply a bias voltage to the membranes of the one ormore CMUTs based at least in part on the collapse voltages of the one ormore CMUTs.

In some embodiments, each of the measurements of the parameter relatedto the capacitances of the one or more CMUTs in the ultrasound deviceincludes a measurement of a time for a ramp voltage to cross a referencevoltage, and where a current is integrated onto one of the one or moreCMUTs to generate the ramp voltage when a particular bias voltage of themultiple bias voltages is applied to the CMUT. In some embodiments, themethod further includes computing the capacitances of the one or moreCMUTs in the ultrasound device based on the measurements of theparameter related to the capacitances of the one or more CMUTs in theultrasound device. In some embodiments, determining the collapsevoltages of the one or more CMUTs based on the capacitances of the oneor more CMUTs at each of the multiple bias voltages, includesdetermining a particular bias voltage at which a discontinuity occurs ina curve of capacitance versus bias voltage for each of the one or moreCMUTs. In some embodiments, the method further includes averaging thecollapse voltages of the one or more CMUTs to produce an average of thecollapse voltages. In some embodiments, causing the ultrasound device toapply the bias voltage to the membranes of the one or more CMUTs basedat least in part on the collapse voltages of the one or more CMUTsincludes causing the ultrasound device to apply a bias voltage to themembranes of the one or more CMUTs that is greater than the average ofthe collapse voltages by an offset voltage. In some embodiments, themembranes of the one or more CMUTs include one shared membrane. In someembodiments, the offset voltage is approximately equal to or between25-30V. In some embodiments, the method further includes using differentoffset voltages when the ultrasound device is imaging differentanatomical regions.

According to another aspect of the application, an apparatus includes aprocessing device in operative communication with an ultrasound device,the processing device configured to: receive, from the ultrasound devicesets of measurements of a capacitance or a parameter related to thecapacitance of one or more CMUTs in the ultrasound device at each ofmultiple bias voltages applied to the membranes of the one or moreCMUTs; and generate a notification based on the sets of measurements.

In some embodiments, each of the measurements of the parameter relatedto the capacitances of the one or more CMUTs in the ultrasound deviceincludes a measurement of a time for a ramp voltage to cross a referencevoltage, and where a current is integrated onto one of the CMUTs togenerate the ramp voltage when a particular bias voltage of the multiplebias voltages is applied to the CMUT. In some embodiments, theprocessing device is further configured to compute the capacitances ofthe one or more CMUTs in the ultrasound device based on the measurementsof the parameter related to the capacitances of the one or more CMUTs inthe ultrasound device. In some embodiments, the processing device isfurther configured to count a number of the CMUTs having a membranestuck to a substrate. In some embodiments, the processing device isconfigured, when counting the number of the CMUTs having a membranestuck to a substrate, to count a number of the CMUTs lacking adiscontinuity in a curve of capacitance versus bias voltage for each ofthe one or more CMUTs. In some embodiments, the processing device isconfigured to generate the notification based on the sets ofmeasurements when the number of the CMUTs, a percentage of the CMUTsmeasured, and/or a percentage of the CMUTs in an array of the ultrasounddevice have a membrane stuck to the substrate. In some embodiments, thenotification includes a notification that the ultrasound device shouldbe replaced. In some embodiments, the processing device is configured,when generating the notification, to generate the notification on adisplay screen of the processing device. In some embodiments, theprocessing device is configured, when generating the notification, totransmit the notification to a supplier of the ultrasound device.

According to another aspect of the application, a method includesreceiving, by a processing device in operative communication with anultrasound device and from the ultrasound device, sets of measurementsof a capacitance or a parameter related to the capacitance of one ormore CMUTs in the ultrasound device at each of multiple bias voltagesapplied to the membranes of the one or more CMUTs; and generating anotification based on the sets of measurements.

In some embodiments, each of the measurements of the parameter relatedto the capacitances of the one or more CMUTs in the ultrasound deviceincludes a measurement of a time for a ramp voltage to cross a referencevoltage, and where a current is integrated onto one of the CMUTs togenerate the ramp voltage when a particular bias voltage of the multiplebias voltages is applied to the CMUT. In some embodiments, the methodfurther includes computing the capacitances of the one or more CMUTs inthe ultrasound device based on the measurements of the parameter relatedto the capacitances of the one or more CMUTs in the ultrasound device.In some embodiments, the method further includes counting a number ofthe CMUTs having a membrane stuck to a substrate. In some embodiments,counting the number of the CMUTs having a membrane stuck to a substrateincluding counting a number of the CMUTs lacking a discontinuity in acurve of capacitance versus bias voltage for each of the one or moreCMUTs. In some embodiments, generating the notification is performedbased on the sets of measurements when the number of the CMUTs, apercentage of the CMUTs measured, and/or a percentage of the CMUTs in anarray of the ultrasound device have a membrane stuck to the substrate.In some embodiments, the notification includes a notification that theultrasound device should be replaced. In some embodiments, generatingthe notification includes generating the notification on a displayscreen of the processing device. In some embodiments, generating thenotification includes transmitting the notification to a supplier of theultrasound device.

According to another aspect of the application, an ultrasound deviceincludes receive circuitry having an input terminal, a capacitor coupledto the input terminal of the receive circuitry, and a current sourcecouplable to the input terminal of the receive circuitry.

In some embodiments, the current source comprises a first current sourceconfigured to supply current to the capacitor and thereby generate afirst ramp voltage at the input terminal of the receive circuitry, andthe ultrasound device further comprises a second current sourcecouplable to the input terminal of the receive circuitry and configuredto sink current from the capacitor and thereby generate a second rampvoltage at the input terminal of the receive circuitry. In someembodiments, the receive circuitry is capable of being configured as aunity-gain amplifier. In some embodiments, the receive circuitry, thecapacitor, and the current source are disposed within a single package.In some embodiments, the current source and the capacitor are disposedon a same semiconductor chip as the receive circuitry. In someembodiments, the current source and the capacitor comprise a built-inself-test (BIST) circuit.

According to another aspect of the application, a method for testingreceive circuitry in an ultrasound device includes operating a currentsource in the ultrasound device to inject a current to an input terminalof the receive circuitry in the ultrasound device, wherein the inputterminal is electrically coupled to a capacitor.

In some embodiments, injecting the current to the input terminal of thereceive circuitry comprises charging or discharging the capacitor togenerate a ramp voltage at an input terminal of the receive circuitry.In some embodiments, the receive circuitry is configured to operate as aunity-gain amplifier. In some embodiments, the receive circuitry, thecapacitor, and the current source are disposed within a single package.In some embodiments, the current source and the capacitor are disposedon a same semiconductor chip as the receive circuitry. In someembodiments, the current source and the capacitor comprise a built-inself-test (BIST) circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and embodiments will be described with reference to thefollowing exemplary and non-limiting figures. It should be appreciatedthat the figures are not necessarily drawn to scale. Items appearing inmultiple figures are indicated by the same or a similar reference numberin all the figures in which they appear.

FIG. 1 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 2 illustrates transistor symbols used for the three different typesof transistors, in accordance with certain embodiments described herein;

FIG. 3 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 4 is an example schematic diagram illustrating further circuitry inan ultrasound system, in accordance with certain embodiments describedherein;

FIG. 5 is an example circuit diagram for a transconductance amplifier,in accordance with certain embodiments described herein;

FIG. 6 is a circuit diagram of a non-limiting example of thetransconductance amplifier of FIG. 5 , in accordance with certainembodiments described herein;

FIG. 7 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 8 is an example schematic diagram illustrating further circuitry inan ultrasound system, in accordance with certain embodiments describedherein;

FIG. 9 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 10 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 11 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 12 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 13 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 14 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 15 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 16A is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 16B is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 17 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 18 is a circuit diagram of an example capacitor network, inaccordance with certain embodiments described herein;

FIG. 19 is a circuit diagram of another example capacitor network, inaccordance with certain embodiments described herein;

FIG. 20 is a circuit diagram of another example capacitor network, inaccordance with certain embodiments described herein;

FIG. 21 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein;

FIG. 22 is a circuit diagram of an example capacitor network, inaccordance with certain embodiments described herein;

FIG. 23 is a circuit diagram of an example capacitor network, inaccordance with certain embodiments described herein;

FIG. 24 is a circuit diagram of another example capacitor network, inaccordance with certain embodiments described herein;

FIG. 25 is a circuit diagram of an example capacitor network, inaccordance with certain embodiments described herein;

FIG. 26 is a circuit diagram of another example capacitor network, inaccordance with certain embodiments described herein;

FIG. 27 is a block diagram of an ultrasound circuitry, in accordancewith certain embodiments described herein;

FIG. 28 is a block diagram of another example of ultrasound circuitry,in accordance with certain embodiments described herein;

FIG. 29 is a block diagram of another example of ultrasound circuitry,in accordance with certain embodiments described herein;

FIG. 30 is a block diagram of another example of ultrasound circuitry,in accordance with certain embodiments described herein;

FIG. 31 is a block diagram of another example of ultrasound circuitry,in accordance with certain embodiments described herein;

FIG. 32 is a block diagram of another example of ultrasound circuitry,in accordance with certain embodiments described herein;

FIG. 33 is a block diagram of another example of ultrasound circuitry,in accordance with certain embodiments described herein;

FIG. 34 is a block diagram of another example of ultrasound circuitry,in accordance with certain embodiments described herein;

FIG. 35A illustrates a flow diagram for a process for testing a pulserin an ultrasound device, in accordance with certain embodimentsdescribed herein;

FIG. 35B illustrates a flow diagram for a process for testing receivecircuitry in an ultrasound device, in accordance with certainembodiments described herein;

FIG. 36 illustrates a flow diagram for a process for testing a pulser inan ultrasound device, in accordance with certain embodiments describedherein;

FIG. 37 illustrates a flow diagram for a process for characterizing acapacitive micromachined ultrasonic transducer (CMUT), in accordancewith certain embodiments described herein;

FIG. 38 illustrates a flow diagram for a process for testing a pulser inan ultrasound device, in accordance with certain embodiments describedherein;

FIG. 39 illustrates a process for performing measurements in order todetermine the collapse voltage of a CMUT, in accordance with certainembodiments described herein;

FIG. 40 illustrates a process for determining the collapse voltages ofone or more CMUTs and applying a bias voltage to the CMUTs, inaccordance with certain embodiments described herein;

FIG. 41 illustrates a process for generating a notification based onmeasurements of capacitance of CMUTs, in accordance with certainembodiments described herein;

FIG. 42 illustrates a schematic diagram of a CMUT, in accordance withcertain embodiments described herein;

FIG. 43 illustrates another schematic diagram of the CMUT of FIG. 42 ,in accordance with certain embodiments described herein;

FIG. 44 illustrates a schematic block diagram of an example ultrasoundsystem upon which various aspects of the technology described herein maybe practiced;

FIG. 45 illustrates an example handheld ultrasound probe, in accordancewith certain embodiments described herein;

FIG. 46 illustrates an example wearable ultrasound patch, in accordancewith certain embodiments described herein; and

FIG. 47 illustrates an example ingestible ultrasound pill, in accordancewith certain embodiments described herein.

DETAILED DESCRIPTION

Certain ultrasound devices include ultrasonic transducers, such ascapacitive micromachined ultrasonic transducers (CMUTs), that areconfigured to convert a voltage pulse signal to an ultrasonic wave. Togenerate an ultrasonic wave of sufficient pressure to penetrate a humanbody, a pulser circuit may generate a high-voltage pulse signal andinput that high-voltage pulse signal to a CMUT.

Certain ultrasound devices also include receive circuitry which mayinclude amplifiers, filters, analog-to-digital converters, and digitalprocessing circuits that are configured to receive, process, and outputelectronic signals produced by ultrasonic transducers in response toreceived ultrasonic waves. When there are multiple channels of receivecircuitry, it may be helpful for the receive circuitry to operate at lowvoltages. For example, this may enable receive circuitry to achieve asmall physical size in an integrated circuit, and may help to preventthe receive circuitry from generating too much heat. Ultrasound devicesmay therefore have high-voltage (HV) domains including, for example,pulsers, and a low-voltage (LV) domains including, for example, receivecircuitry.

It may be helpful to test pulsers in integrated circuits. For example,testing may include:

-   -   1. Analyzing whether a pulser is working (e.g., whether it is        pulsing)    -   2. When there are multiple pulsers in an ultrasound device,        analyzing whether certain pulsers are working and certain        pulsers are not working;    -   3. Analyzing what a pulser output waveform looks like, which may        be especially helpful for multi-level pulsing and for imaging        optimization;    -   4. When there are multiple pulsers in the ultrasound device,        analyzing how uniform pulsed waveforms are among different        pulsers;    -   5. Analyzing what the actual slew rate of a pulser is with        different CMUT loads.

Certain methods of testing pulsers, such as measuring acoustictransmission power from the pulsers using lens reflection, may sufferfrom lens nonuniformity, and may not be capable of measuring the realpulser output waveform.

The inventors have recognized that one efficient approach for testing apulser may be to route the output of the pulser to the ultrasounddevice's receive circuitry, which may already be configured to processelectronic signals and output the electronic signals to an externaldevice, where the signals can be analyzed. However, a challenge is thatsignals output by the pulser may be high-voltage while the receivecircuitry may only be capable of handling low-voltage signals. Theinventors have recognized that built-in self-test (BIST) integratedcircuitry may be integrated onto the same substrate (e.g., asemiconductor substrate) that also includes integrated ultrasoundcircuitry, such as one or more pulsers, where the BIST circuitry may beconfigured to receive high-voltage signals from a pulser and attenuatethe signal such that the signal may be processed and output by thereceive circuitry. One approach, which may be considered a current-modeapproach, includes converting the high-voltage pulser output signal toan attenuated current signal using a transconductance amplifier coupledbetween the pulser and the receive circuitry, and then using atransimpedance amplifier in the receive circuitry to convert theattenuated current signal to a low-voltage signal. Another approach,which may be considered a voltage-mode approach, includes converting thehigh-voltage pulser output signal to an attenuated voltage signal usingone or more capacitor dividers in a capacitor network between the pulserand the receive circuitry.

It should be noted that in some embodiments, a pulser may alreadyinclude attenuation circuitry (e.g., a capacitor divider) forattenuating the high-voltage pulser output signal to a mid-voltagepulser output. Feedback circuitry in the pulser that operates at amid-voltage level (i.e., a level between the high-voltage level of thepulser output and the low-voltage levels of the receive circuitry) maythen use the attenuated pulser output signal. Thus, the pulser mayinclude both an HV domain and a mid-voltage (MV) domain. In suchembodiments, in the current-mode approach, the BIST circuitry mayconvert the MV version of the pulser output signal to a current signal,and then the transimpedance amplifier may convert the current signal toa LV signal. In voltage mode, the BIST circuitry may convert the MVversion of the pulser output signal to a LV signal.

The inventors have also recognized that such circuitry for BIST may alsobe used for characterizing a CMUT (e.g., characterizing its capacitance,collapse voltage, and/or stiction) and/or testing receive circuitry. Forexample, a transconductance amplifier in BIST circuitry may be used togenerate a constant current and inject that current to an input terminalof a comparator in receive circuitry in the ultrasound device, where theinput terminal of the comparator is electrically coupled to the CMUT.The constant current output from the transconductance amplifier may beintegrated onto the CMUT to generate a ramp voltage. The comparator maycompare the ramp voltage to the reference voltage, and the time it takesfrom the beginning of the ramp to when the ramp crosses the referencevoltage may be used to compute the capacitance of the CMUT. If thecapacitance of a CMUT is measured as a function of multiple bias voltageapplied to the CMUT, the collapse voltage of the CMUT may be determined,or it may be determined whether the membrane of the CMUT is stuck to thesubstrate of the CMUT.

Measuring the collapse voltage may be helpful because the collapsevoltage of a CMUT may change with time. Applying a bias voltage to theCMUT that is a particular offset voltage greater than the collapsevoltage of the CMUTs may help to ensure that, as the collapse voltage ofthe CMUT changes, the value of the bias voltage applied to the CMUTminus the collapse voltage of the CMUT remains the same. This may helpto keep the acoustic efficiency of the CMUT consistently optimized overtime. When an ultrasound device includes an array of CMUTs that shareone membrane, the collapse voltages of all the CMUTs in the array, or asubset thereof, may be measured and averaged, and a bias voltage may beapplied to the CMUTs that is a particular offset voltage greater thanthe average of the collapse voltages of the CMUTs.

With regards to stiction, a CMUT membrane can get stuck on the substratedue to electrostatic force from charges trapped in the cavity, or fromvan der Waals forces between the membrane and the bottom of the cavity.Such stiction is detrimental to the operation of the CMUT. Byrestricting the motion of the membrane, stiction may cause a lowertransmission pressure output as well as decreased reception sensitivity,such that resulting ultrasound images may be lower in quality (e.g., interms of signal-to-noise ratio (SNR)). Also, in an array of CMUTs,stiction may cause non-uniformity in the array, since some CMUTs mightbe stuck while others may not. The pattern of stuck CMUTs may also notrepeat. Asymmetry in the stiction profile may cause undesirable resonantmodes. Non-uniformity and non-repeatability in the stiction profile mayparticularly negatively affect some imaging modes such as Doppler modeby introducing imaging artifacts. It may be helpful to measure how manyCMUTs in an array are stuck and generate a notification when the numberof stuck CMUTs exceeds a threshold. For example, the notification maynotify a user that the ultrasound device should be replaced.

For testing receive circuitry, a pulser may generate a multi-level pulsevoltage waveform (e.g., to mimic a sinewave test waveform) and thetransconductance amplifier in the BIST circuitry may convert thisvoltage waveform to a current waveform and output this current waveformto the receive circuitry. This may be an accurate and controllablemethod for injecting a test waveform to the receive circuitry.Additionally, when multiple blocks of circuitry include transconductanceamplifiers, this method may allow for uniformity in generation ofwaveforms and testing based on the waveforms across the differentblocks. In some embodiments, for testing receive circuitry, currentsources coupled through switches to a capacitor at the input of receivecircuitry may be operated to charge or discharge the capacitor andthereby generate an increasing and/or decreasing ramp voltages at theinput of the receive circuitry. This ramp voltage may be injected to thereceive circuitry and used for testing the receive circuitry.

As referred to herein in the detailed description and claims, twoelements being “coupled” should be understood to mean either directlycoupled or that there may be intervening circuitry between the twoelements.

Various aspects of the present disclosure may be used alone, incombination, or in a variety of arrangements not specifically describedin the embodiments described in the foregoing and is therefore notlimited in its application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

FIG. 1 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 1 includes a pulser 100, a capacitive micromachinedultrasonic transducer (CMUT) 152, a receive switch 162, and receivecircuitry 184. The pulser 100 is coupled to the CMUT 152. The CMUT 152is in series with the receive switch 162, which is coupled to thereceive circuitry 184. The CMUT 152 is couplable to the receivecircuitry 184 by closing the switch 162.

In operation, the pulser 100 may be configured to generate high-voltagepulses that are inputted to the CMUT 152 (during the “transmit phase”).The high-voltage pulses may cause the CMUT 152 to output ultrasonicwaves. During the transmit phase, to prevent the high-voltage pulsesfrom the pulser 100 from being inputted to the receive circuitry 184,which operates at low voltages, the receive switch 162 may be configuredto be open. The CMUT 152 may be configured to receive reflectedultrasonic waves and convert these ultrasonic waves to electric currents(during the “receive phase”). The receive circuitry 184 may beconfigured to convert these electric currents to voltages that can befurther processed by other circuitry in the receive circuitry 184.During the receive phase, to allow electric currents converted fromreceived ultrasonic waves to be inputted to the receive circuitry 184,the receive switch 162 may be configured to be closed. The receivecircuitry 184 may include further amplifiers, filters, analog-to-digitalconverters, and digital processing circuits that may be configured toreceive, process, and output the electronic signals produced by the CMUT152 in response to received ultrasonic waves.

FIGS. 3, 4, 8, 10, 14, 15, 16, 17, and 21 illustrate non-limitingexamples of the circuitry of FIG. 1 in more detail. The below figuresinclude three types of transistors: high-voltage (HV), mid-voltage (MV),and low-voltage (LV). FIG. 2 illustrates transistor symbols used for thethree different types of transistors, in accordance with certainembodiments described herein. In some embodiments, the maximum operatingvoltage for HV transistors may be up to 80 V. For example, the maximumoperating voltage may be 32 V or 55 V. In some embodiments, the maximumoperating voltage for MV transistors may be up to 8 V. For example, themaximum operating voltage may be 8 V or 5 V. In some embodiments, themaximum operating voltage for LV transistors may be up to 3.3 V. Forexample, the maximum operating voltage may be 1.5 V or 1.1 V. The belowfigures also include three types of power supplies: HV, MV, and LV,where the voltage of the HV power supplies (or the absolute value oftheir voltage) is higher than the voltage of the MV power supplies (orthe absolute value of their voltage), and the voltage of the MV powersupplies (or the absolute value of their voltage) is higher than thevoltage of the LV power supplies (or the absolute value of theirvoltage).

FIG. 3 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 3 includes a pulser 300 (which may be an example of thepulser 100), the capacitive micromachined ultrasonic transducer (CMUT)152, the receive switch 162, and receive circuitry 384 (which may be anexample of the receive circuitry 184). The pulser 300 includes acomparator 302, a controller 310, a level shifter 316, a HV n-typemetal-oxide-semiconductor field effect transistor (nMOS) 326, a HVp-type metal-oxide-semiconductor field effect transistor (pMOS) 334, anda capacitor divider formed by two capacitors 346 and 348. The receivecircuitry 384 includes an amplifier 364 and other circuitry notexplicitly illustrated. As will be described further below, in someembodiments the amplifier 364 in the receive circuitry 384 isconfigurable as a transimpedance amplifier. In some embodiments, theamplifier 364 in the receive circuitry 384 is configurable as acomparator. In some embodiments, the amplifier 364 in the receivecircuitry 384 is configurable as a unity-gain amplifier.

The comparator 302 has a positive input terminal 304, a negative inputterminal 306, and an output terminal 308. The controller 310 has aninput terminal 312, a positive output terminal 314, and a negativeoutput terminal 315. The level shifter 316 has a positive input (inp)terminal 318, a negative input terminal (inn) 320, a positive outputterminal (outp) 322, and a negative output terminal (outn) 324. The HVnMOS 326 has a gate terminal 328, a drain terminal 330, and a sourceterminal 332. The HV pMOS 334 has a gate terminal 336, a drain terminal338, and a source terminal 340. The amplifier 364 has a positive inputterminal 366, a negative input terminal 368, and an output terminal 370.

The positive input terminal 304 of the comparator 302 is coupled to anode Sense. The negative input terminal 306 of the comparator 302 iscoupled to a node Thres. The output terminal 308 of the comparator 302is coupled to the input terminal 312 of the controller 310. The positiveoutput terminal 314 of the controller 310 is coupled to the positiveinput terminal 318 of the level shifter 316. The negative outputterminal 315 of the controller 310 is coupled to the negative inputterminal 320 of the level shifter 316. The negative output terminal 324of the level shifter 316 is coupled to the gate terminal 328 of the HVnMOS 326. The positive output terminal 322 of the level shifter 316 iscoupled to the gate terminal 336 of the HV pMOS 334. The drain terminal330 of the HV nMOS 326 is coupled to the node Out. The source terminal332 of the HV nMOS 326 is coupled to a HV negative power supply 344. Thedrain terminal 338 of the HV pMOS 334 is coupled to the node Out. Thesource terminal 340 of the HV pMOS 334 is coupled to a HV positive powersupply 342. The capacitor 346 extends between the node Out and the nodeSense. The capacitor 348 extends between the node Sense and ground 350.

The CMUT 152 is coupled between the node Out and a bias voltage 372. Inparticular, a bottom electrode of the CMUT 152 at its substrate may becoupled to the node Out and a membrane of the CMUT 152 may be coupled tothe bias voltage 372, which may be referred to as V_(BIAS). If Out is ata virtual ground, then the voltage applied to the CMUT 152 (i.e.,between the membrane and the bottom electrode of the CMUT 152) may beV_(BIAS). The receive switch 162 is coupled between the node Out and thenegative input terminal 368 of the amplifier 364. The CMUT 152 iscouplable to the input terminal of the receive circuitry 384 (in FIG. 3, to the negative input terminal 368 of the amplifier 364) by closingthe receive switch 162.

A bias voltage Vref is coupled to the positive input terminal 366 of theamplifier 364. Vref may be generated by bias circuitry, such as aresistor divider in parallel with a bypass capacitor. A resistor 380 inseries with a switch 1013 is coupled between the negative input terminal368 of the amplifier 364 and the output terminal 370 of the amplifier364. A switch 1031 is also coupled between the negative input terminal368 of the amplifier 364 and the output terminal 370 of the amplifier364. In FIG. 3 , the switch 1013 is closed and the switch 1031 is open.This configuration, in which the resistor 380 is coupled in feedbackconfiguration between the negative input terminal 368 of the amplifier364 and the output terminal 370 of the amplifier 364 is referred to asthe TIA 365.

In operation, the pulser 300 may be configured to generate high-voltagepulses at the node Out. The node Out is coupled to the CMUT 152, suchthat the high-voltage pulses at Out may cause the CMUT 152 to outputultrasonic waves. The pulser 300 may operate in a feedback configurationto output these high-voltage pulses. In particular, the capacitordivider consisting of the capacitors 346 and 348 may be configured toattenuate the output voltage of the pulser 300 at the node Out to alower voltage at the node Sense. The capacitor divider may be configuredto attenuate the high-voltage pulses in the HV domain to lower-voltagepulses in the MV domain appropriate for processing by the comparator 302and the controller 310, which may operate at voltages in the MV domain.

The comparator 302 may be configured to compare the voltage at Sense tothe voltage at the node Thres. As will be described further below, thevoltage at the node Thres may be a threshold voltage. The comparator 302may be configured to output a high voltage if Sense is greater thanThres and output a low voltage if Sense is less than Thres. Thecontroller 310 may be configured to control the voltages inputted to thelevel shifter 316 based on the output voltage received from thecomparator 302. For example, if the output voltage received from thecomparator 302 is high (i.e., the voltage at Sense is greater than thevoltage at Thres), then the controller 310 may be configured to outputsignals at the positive output terminal 314 and/or at the negativeoutput terminal 315 configured to turn on the HV nMOS 326 and/or to turnoff the HV pMOS 334. In this case, an electric current flowing from thenode Out to the HV negative power supply 344 may discharge or negativelycharge the node Out until the voltage at Sense is equal to (or within athreshold of) the voltage at Thres. As another example, if the outputvoltage received from the comparator 302 is low, then the controller 310may be configured to output signals at the positive output terminal 314and/or at the negative output terminal 315 configured to turn off the HVnMOS 326 and/or to turn on the HV pMOS 334. In this case, an electriccurrent flowing from the HV positive power supply 342 may charge thenode Out until the voltage at Sense is equal to (or within a thresholdof) the voltage at Thres. As can be seen in FIG. 3 , the output signalsat the positive output terminal 314 and at the negative output terminal315 of the controller 310 are not directly coupled to the HV nMOS 326and the HV pMOS 334. This may be because the controller 310 may operateat voltages in the MV domain and the HV nMOS 326 and the HV pMOS mayoperate at voltages in the HV domain. Thus, the level shifter 316 may beconfigured to receive these output signals in the MV domain at itspositive input terminal 318 and negative input terminal 320, and convertthese signals to higher voltage signals in the HV domain at the positiveoutput terminal 322 and the negative output terminal 324 appropriate forcontrolling the gate terminal 328 of the HV nMOS 326 and the gateterminal 336 of the HV pMOS 334. If the voltage at Sense equals thevoltage at Thres, the comparator 302 may be turned off (e.g., by controllogic not illustrated) until the voltage at Thres changes. Forrail-to-rail two-level bipolar or unipolar pulsing, the feedback networkformed by the comparator 302, the controller 310, the level shifter 316,and the capacitors 346 and 348 may not be used.

In addition to transmitting ultrasonic waves in response to receivinghigh-voltage pulses from the pulser 300 (during the “transmit phase”),the CMUT 152 may be configured to receive reflected ultrasonic waves andconvert these ultrasonic waves to electric currents (during the “receivephase”). The TIA 365 may be configured to convert these electriccurrents to voltages that can be further processed by other circuitry inthe receive circuitry 384. During the transmit phase, to prevent thehigh-voltage pulses from the pulser 300 from being inputted to the TIA365, the receive switch 162 may be configured to be open. During thereceive phase, to allow electric currents converted from receivedultrasonic waves to be inputted to the TIA 365 (and specifically, to thenegative input terminal 368 of the amplifier 364), the receive switch162 may be configured to be closed.

With the resistor 380 coupled in feedback around its amplifier 364, theTIA 365 may be configured to convert the current received at thenegative input terminal 368 of the amplifier 364 to a voltage at theoutput terminal 370 of the amplifier 364 with a gain equivalent (atleast approximately) to the resistance of the resistor 380. The voltageat the output terminal 370 may be output to other circuitry in thereceive circuitry 384, which may include, for example, circuitry forconverting analog voltages to digital codes and for outputting thedigital codes to an external device.

FIG. 4 is an example schematic diagram illustrating further circuitry inan ultrasound system, in accordance with certain embodiments describedherein. FIG. 4 is the same as FIG. 3 , but with the addition of atransconductance amplifier (Gm) 454 coupled between the pulser 300 andthe receive circuitry 384. As described above, it may be helpful toanalyze the output of the pulser 300 for testing purposes. While thereceive circuitry 384 may be capable of converting analog voltages todigital codes and outputting the digital codes to an external devicewhere they can be analyzed, it may not be feasible to directly connectthe output of the pulser 300 to the receive circuitry 384 (e.g., to theTIA 365). The output of the pulser 300 may include pulses that arehigher in voltage (e.g., in the HV domain) than the operating voltage ofthe receive circuitry 384 (e.g., in the LV domain). The inventors haverecognized that, instead, the transconductance amplifier 454 may beincluded between the pulser 300 and the receive circuitry 384 (inparticular, the TIA 365) for built-in self-testing (BIST). Thetransconductance amplifier 454 may be configured to convert the outputof the pulser 300 (or an attenuated version of the output of the pulser300) to an attenuated current signal that can be converted to a voltagesignal by the TIA 365. For example, the transconductance amplifier maybe configured to convert the HV output of the pulser 300, or anattenuated version of the pulser 300 output in the MV domain, to the LVdomain. This LV analog signal may then be output to other circuitry inthe receive circuitry 384, which may be configured to convert the analogvoltage signal to a digital codes and output it to an external device,where it can be analyzed for testing purposes. In other words, thetransconductance amplifier may be configured to process the output ofthe pulser 300 such that the receive circuitry 384 may be reused fortesting. FIG. 4 may thus illustrate a configuration for testing of thepulser 300. As will be described further below, the transconductanceamplifier 454 may be a linearized transconductance amplifier.

The transconductance amplifier 454 has a positive input terminal 456, anegative input terminal 458, and an output terminal 460. The positiveinput terminal 456 of the transconductance amplifier 454 is coupled tothe node Sense. The negative input terminal 458 is coupled the nodeThres0. The output terminal 460 of the transconductance amplifier 454 iscoupled to the negative input terminal 368 of the amplifier 364. Theamplifier 364, as in FIG. 3 , is in the feedback (current-to-voltageconversion) configuration of the TIA 365. The transconductance amplifier454 may be configured to receive the voltage pulses from the pulser 300(after attenuation by the capacitor divider formed by the capacitors 346and 348) and convert the difference between these voltage pulses and thevoltage Thres0 at the negative input terminal 458 to a current at theoutput terminal 460. This current may then be input to the TIA 365 (inparticular, to the negative input terminal 368 of the amplifier 364) forconversion to an analog voltage that may be digitally converted andoutputted to an external device by the receive circuitry 384, andanalyzed for testing purposes.

As described above, the transconductance amplifier 454 may be configuredto convert the difference between the voltage pulses at Sense and thevoltage Thres0 to a current. As will be described further below, thevoltage Thres0 may be the middle voltage of the voltage pulses at Sense,such that subtracting Thres0 from the voltage at Sense may remove the DCcomponent of the voltage pulses. If the DC component of the voltagepulses were not removed, the output current of the transconductanceamplifier 454 may saturate the TIA 365.

FIG. 5 is an example circuit diagram for the transconductance amplifier454, in accordance with certain embodiments described herein. Thetransconductance amplifier 454 includes a positive input MV transistor586, a negative input MV transistor 588, a current mirror 590, a currentmirror 592, a current mirror 594, a resistor 596, and a resistor 598.The gate of the positive input MV transistor 586, which is also thepositive input terminal 456 of the transconductance amplifier 454, iscoupled to Sense, the drain is coupled to the current mirror 590, andthe source is coupled to the resistor 596. The gate of the negativeinput MV transistor 588, which is also the negative input terminal 458of the transconductance amplifier 44, is coupled to Thres0, the drain iscoupled to the current mirror 592, and the source is coupled theresistor 598. The current mirror 590 is coupled between the positiveinput MV transistor 586, the current mirror 594, and a MV positive powersupply 543. The current mirror 592 is coupled between the negative inputMV transistor 588, the current mirror 594, and the MV positive powersupply 543. The current mirror 594 is coupled between the current mirror590, the current mirror 592, and ground 350. The output terminal 460 ofthe transconductance amplifier 454 is taken from the node between thecurrent mirror 590 and the current mirror 594 which, in turn, mirrorsthe current from current mirror 592. The current mirror 590 and thecurrent mirror 592 include MV transistors. The current mirror 594includes LV transistors. The resistance of the resistors 596 and 598 isreferred to as R_(s). While FIG. 5 illustrates one example circuit forthe transconductance amplifier 454, it should be appreciated that othercircuits may be used.

The transconductance amplifier 454 of FIG. 5 may be considered asource-degenerated linearized transconductance cell. “Linearized” maymean that the transconductance of the transconductance amplifier 454 isnot dominated by the transconductance (gm) of the positive input MVtransistor 586 and the negative input MV transistor 588, which may bethe normal case for transconductance amplifiers. Rather, thetransconductance of the transconductance amplifier 454 may be dominatedby the resistance R_(s) of the degenerated resistors 596 and 598. Thismay be helpful because gm may not be constant versus different operatingvoltages/currents, which may introduce non-linearity. In contrast, whenthe transconductance is dominated by the resistance R_(s), thetransconductance may be relatively consistent with differentvoltage/current ranges, thus resulting in better linearity. Such alinearized transconductance amplifier may not be used in otherapplications because, to obtain a high voltage gain, gm should dominatethe transconductance. Here, however, the linearity in conversion betweencurrent and voltage may be more important than high gain.

The conversion ratio between the pulser output voltage at the node Outand the transconductance amplifier 454 output at the output terminal 360may be

${A_{capdiv} = \frac{R_{TIA}}{n \cdot R_{s}}},$where A_(capdiv) is the division ratio of the capacitor divider formedby the capacitors 346 and 348, and the current mirror ratio of thecurrent mirrors 590 and 592 is n:1. In particular, for every n paralleltransistors (not illustrated explicitly) in the current mirrors 590 and592 that have their drains connected to their gates, there may be 1transistor that does not have its drain connected to its gate. Toachieve a desired value for the denominator in the expression

$\frac{R_{TIA}}{n \cdot R_{s}},$the current mirror ratio n:1 may be selected (in other words, the numberof parallel transistors may be selected) such that the resistance R_(S)may be a sufficiently low value to achieve an acceptably low requiredphysical area for the resistors 596 and 598. In some embodiments, theratio

$\frac{R_{TIA}}{n \cdot R_{s}}$may be approximately equal to or between 1/20 and 1. In someembodiments, A_(capdiv) may be approximately equal to or between 1/32and ¼ (e.g., ⅛).

FIG. 6 is a circuit diagram of a non-limiting example of thetransconductance amplifier 454, in accordance with certain embodimentsdescribed herein. In particular, FIG. 6 illustrates circuitry, inparticular transistors M9, M10, M11, M12, and M13, with which thecircuitry illustrated in FIG. 5 may be augmented to enable turning onand off of the transconductance amplifier 454. For example, for testingcircuitry in the ultrasound device (e.g., for testing the pulser 300 orfor characterizing the CMUT 152), the transconductance amplifier 454 maybe turned on. For using the ultrasound device for normal imaging, thetransconductance amplifier 454 may be turned off while the pulser 300and the receive circuitry 384 remain on.

In operation, to turn off the transconductance amplifier 454, the signalen may be switched low and the signal en_b may be switched high. Thismay cause:

-   -   1. The transistor M9 to turn on, thereby pulling the drain of M9        low to the ground 350 and turning off the transistors M8 and M9        in the current mirror 594;    -   2. The transistor M10 to turn off, thereby disabling current        flow in its branch of the transconductance amplifier 454;    -   3. The transistor M11 to turn on, thereby pulling the drain of        M11 up to the voltage of the MV power supply 543, and turning        off the transistors M5 and M6 in the current mirror 592;    -   4. The transistor M12 to turn off, thereby disabling current        flow in its branch of the transconductance amplifier 454;    -   5. The transistor M13 to turn on, thereby pulling the drain of        M13 up to the voltage of the MV power supply 543, and turning        off the transistors M3 and M4 in the current mirror 590.

In operation, to turn on the transconductance amplifier 454, the signalen may be switched high and the signal en_b may be switched low. Thismay cause:

-   -   1. The transistor M9 to turn off;    -   2. The transistor M10 to turn on, thereby enabling current flow        in its branch of the transconductance amplifier 454;    -   3. The transistor M11 to turn off;    -   4. The transistor M12 to turn on, thereby enabling current flow        in its branch of the transconductance amplifier 454;    -   5. The transistor M13 to turn off.

In some embodiments, the enable signals for M9, M10, and M11 may beindependent of the enable signals for M12 and M13. For example, theenable signals for M9, M10, and M11 may be switched low while theenabled signals for M12 and M13 may be switched high. This may allowconversion of the voltage at Sense to a current without DC subtractionof the voltage at Thres.

FIG. 7 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 7 illustrates a configuration which may be used for testingof the pulser 300 in conjunction with the configuration illustrated inFIG. 4 . FIG. 7 illustrates the comparator 302, the transconductanceamplifier 454, a resistor ladder 701, and a multiplexer 703. Theresistor ladder 701 includes multiple resistors coupled in a ladderfashion between the HV positive power supply 342 and ground 350 suchthat the resistors form multiple resistor dividers for generatingmultiple voltages at the nodes Thres+2, Thres+1, Thres0, Thres−1,Thres−2. Both the transconductance amplifier 454 and the pulser 300 (inparticular, the comparator 302) are configured to receive, as inputs,voltages from the resistor ladder 701. The multiplexer 703 may acceptthese voltages at its input terminals and select, based on a controlsignal not illustrated, one of the voltages at is output terminal(referred to as the node Thres), which is coupled to the negative inputterminal 306 of the comparator. In some embodiments, the resistor ladder701 may include more resistors for generating more voltage options. Insome embodiments, the resistor ladder 701 may include fewer resistorsfor generating fewer voltage options. The number of voltage optionsgenerated may depend on the requirements for the multi-level pulsing(e.g., how many voltage levels are desired).

As described above, the pulser 300 may operate by using feedback tocause the voltage at the node Sense to be equivalent to, or within athreshold of, the selected threshold voltage at the node Thres. Thevoltage at Sense is an attenuated version of the voltage at the nodeOut, which is the output of the pulser 300. Thus, in operation,selection of one of the voltages generated by the resistor ladder 701may control the output of the pulser 30.

The voltage Thres0 is coupled to the negative input terminal 458 of thetransconductance amplifier 454. As can be seen in FIG. 7 , the voltageThres0 is the middle voltage of the voltages generated by the resistorladder 701, and due to feedback of the pulser 300, Thres0 may be middlevoltage of the voltage at Sense. As described above, subtracting Thres0from the voltage at Sense by the transconductance amplifier 454 mayremove the DC component of the voltage pulses at Sense. If the DCcomponent of the voltage pulses were not removed, the output of thetransconductance amplifier 454 may saturate the TIA 365 (not illustratedin FIG. 7 ).

FIG. 8 is an example schematic diagram illustrating further circuitry inan ultrasound system, in accordance with certain embodiments describedherein. FIG. 8 is the same as FIG. 4 , except that:

-   -   1. The voltage Thres (i.e., the same voltage inputted to        negative input terminal 306 of the comparator 302) is inputted        to the positive input terminal 456 of the transconductance        amplifier 454;    -   2. The switch 1013 and the switch 1031 are open, such that there        is an open circuit between the negative input terminal 368 and        the output terminal 370 of the amplifier 364. In other words,        the amplifier 364 is in open-loop configuration and may operate        as a comparator (rather than as a TIA);    -   3. The receive switch 162 is closed.

FIG. 8 illustrates a non-limiting example of a configuration forcharacterizing the CMUT 152 (e.g., characterizing its capacitance,collapse voltage, and/or stiction). In such a configuration, the pulser300 may be kept off, such that it does not output any high-voltagesignals. The voltage at Thres may be kept constant, such that thevoltage difference between Thres and Thres0 that is inputted to thetransconductance amplifier 454 is constant, and the output current fromthe transconductance amplifier 454 is constant. The constant currentoutput from the transconductance amplifier 454 may be integrated ontothe CMUT 152 to generate a ramp voltage at the negative input terminal368 of the amplifier 364. The amplifier 364, operating as a comparator,may compare the ramp voltage to the reference voltage (referred to asVref) at the positive input terminal 366 of the amplifier 364. When theramp voltage crosses Vref, the output voltage of the amplifier 364 mayswitch from high to low or from low to high. If the ramp begins at thevoltage of an LV positive power supply (referred to as VDDA) andproceeds to ground 350, or if the ramp begins at ground 350 and proceedsto VDDA, the configuration of FIG. 8 may accordingly be used to time howlong it takes from the beginning of the ramp to when the ramp crossVref. The capacitance of the CMUT 152 may be computed as

${C = \frac{I_{ramp} \times T_{ramp}}{{VDDA} - {Vref}}},$where I_(ramp) is the constant current outputted by the transconductanceamplifier 454 and T_(ramp) is the time it takes from the beginning ofthe ramp to when the ramp cross Vref. In some embodiments, two ramps maybe used, one during current sourcing and one during current sinking,such that one ramp proceeds from VDDA to ground 350 (during currentsinking) and one proceeds from ground 350 to VDDA (during currentsourcing), and the average of the T_(ramp) measured for each ramp may beused to compute C. In some embodiments, multiple repeated measurementsof the time for ramp voltages to cross the reference voltage may beperformed during current sourcing, and these multiple measurements oftime may be averaged. Additionally, multiple repeated measurements ofthe time for ramp voltages to cross the reference voltage may beperformed during current sinking, and these multiple measurements oftime may be averaged. The two averaged results, one result for currentsourcing and one for current sinking, may then be averaged together.Alternatively, the multiple measurements from current sourcing and fromcurrent sinking may be averaged together. It should be appreciated thatin some embodiments, measuring the time for a ramp voltage to cross thereference voltage during current sourcing may be performed prior tomeasuring the time for a ramp voltage to cross a reference voltageduring current sinking, while in some embodiments, measuring the timefor a ramp voltage to cross the reference voltage during current sinkingmay be performed prior to measuring the time for a ramp voltage to crossthe reference voltage during current sourcing.

In some embodiments, characterizing the CMUT 152 may includecharacterizing the collapse voltage of the CMUT 152. Characterizing thecollapse voltage of the CMUT 152 may include applying multiple differentbias voltage values V_(BIAS) to the CMUT 152. The bias voltage V_(BIAS)applied to the CMUT may be measured between the membrane of the CMUT 152and the bottom electrode at the substrate of the CMUT 152. If the bottomelectrode at the substrate of the CMUT 152 is at virtual ground, thenapplying V_(BIAS) to the CMUT may be accomplished by applying V_(BIAS)to the membrane. For each value of V_(BIAS), the capacitance of the CMUT152 may be computed as described above to produce a C vs. V_(BIAS)curve. A discontinuity may be observed in this curve when there iscontact between the membrane and the substrate of the CMUT 152. If the Cvs. V_(BIAS) curve was generated by increasing the value of V_(BIAS),then the value of V_(BIAS) at which this contact occurs (i.e., the valueof V_(BIAS) at which the discontinuity occurs) may be the collapsevoltage of the CMUT 152. A discontinuity may be detected in the C vs.V_(BIAS) curve by calculating the first and/or second derivative of thecurve.

In some embodiments, characterizing the CMUT 152 may includecharacterizing whether the membrane of the CMUT 152 is stuck to thesubstrate of the CMUT 152. In some embodiments, a C vs. V_(BIAS) curvemay be generated as described above, and if no discontinuity is detectedin this curve, this may mean that the membrane of the CMUT 152 is stuckto the substrate of the CMUT 152. This may be because, for the entirerange of V_(BIAS) values, the membrane is collapsed.

In some embodiments, applying V_(BIAS) to the membrane of the CMUT 152may include routing the voltage V_(BIAS) from circuitry in theultrasound device but external to the substrate on which the CMUT 152 isdisposed, through a routing network, and to the membrane of the CMUT152. It may be helpful to wait for the voltage at the membrane to settleto V_(BIAS) after charging or discharging the routing network.

FIG. 9 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 9 illustrates a non-limiting example of a configuration forcharacterizing the CMUT 152 in conjunction with the configurationillustrated in FIG. 8 . FIG. 9 is the same as FIG. 7 , except that inFIG. 9 , the voltage Thres is inputted to the positive input terminal456 of the transconductance amplifier 454.

FIG. 10 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 10 is the same as FIG. 4 , except that FIG. 10 includes amultiplexer 1005. The multiplexer 1005 includes a first input terminal1007, a second input terminal 1009, and an output terminal 1011. Thefirst input terminal 1007 is coupled to the node Sense. The second inputterminal 1009 is coupled to the node Thres. The output terminal 1011 iscoupled to the positive input terminal 456 of the transconductanceamplifier 454.

The circuit of FIG. 10 may be used either for testing the pulser 300, asdescribed with reference to FIG. 4 , or for characterizing the CMUT 152,as described with reference to FIG. 8 . In operation, for testing thepulser 300, a control signal for the multiplexer 1005 (not illustratedin the figure) may control the multiplexer 1005 to select the voltage atthe first input terminal 1007 (i.e., the voltage at the node Sense) foroutputting at the output terminal 1011. Additionally, the switch 1013may be closed and the switch 1031 may be open, such that the amplifier364 is in the close-loop, feedback configuration of the TIA 365. Thus,the circuit may be equivalent to the circuit of FIG. 4 . Forcharacterizing the CMUT 152, a control signal for the multiplexer 1005(not illustrated in the figure) may control the multiplexer 1005 toselect the voltage at the second input terminal 1009 (i.e., the voltageat the node Thres) for outputting at the output terminal 1011.Additionally, the switch 1013 and the switch 1031 may be open, such thatthe amplifier 364 is in open-loop, comparator configuration, and thereceive switch 162 may be closed. Thus, the circuit may be equivalent tothe circuit of FIG. 8 .

FIG. 11 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 11 is the same as FIG. 7 , except that FIG. 11 includes achopper switch 1105. The chopper switch 1105 includes a first inputterminal 1107, a second input terminal 1109, a first output terminal1111, and a second output terminal 1113. The first input terminal 1107is coupled to Sense. The second input terminal 1109 is coupled to Thres.The first output terminal 1111 is coupled to the positive input terminal456 of the transconductance amplifier 456. The second output terminal1113 is coupled to the positive input terminal 304 of the comparator302.

The circuit of FIG. 11 may be used either for testing the pulser 300, asdescribed with reference to FIG. 7 , or for characterizing the CMUT 152,as described with reference to FIG. 9 . In operation, for testing thepulser 300, a control signal for the chopper switch 1105 (notillustrated in the figure) may control the chopper switch 1105 to selectthe voltage at the first input terminal 1107 (i.e., at the node Sense)for outputting at the first output terminal 1111. Thus, the circuit maybe equivalent to the circuit of FIG. 7 . For characterizing the CMUT152, the control signal for the chopper switch 1105 (not illustrated inthe figure) may control the chopper switch 1105 to select the voltage atthe second input terminal 1109 (i.e., the voltage at the node Thres) foroutputting at the first output terminal 1111. Thus, the circuit may beequivalent to the circuit of FIG. 9 .

Additionally, in operation, for normal transmission of pulses using thepulser 300, a control signal for the chopper switch 1105 (notillustrated in the figure) may control the chopper switch 1105 to selectthe voltage at the first input terminal 1107 (i.e., the voltage at thenode Sense) for outputting at the second output terminal 1113 and toselect the voltage at the second input terminal 1109 (i.e., the voltageat the node Thres) for outputting at the first output terminal 1111.Alternatively, the control signal for the chopper switch 1105 maycontrol the chopper switch 1105 to select the voltage at the first inputterminal 1107 (i.e., the voltage at the node Sense) for outputting atthe first output terminal 1111 and to select the voltage at the secondinput terminal 1109 (i.e., the voltage at the node Thres) for outputtingat the second output terminal 1113. Thus, the circuit may control thepolarity of pulses generated by the pulser 300, and the comparator 302may only need to detect crossings in one direction (e.g., rising orfalling).

FIG. 12 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 12 is the same as FIG. 7 , except that FIG. 12 includes amultiplexer 1205. The multiplexer 1205 includes a first input terminal1207, a second input terminal 1209, and an output terminal 1211. Thefirst input terminal 1207 is coupled to Sense. The second input terminal1209 is coupled to Thres. The output terminal 1211 is coupled to thepositive input terminal 456 of the transconductance amplifier 456. Senseis also coupled to the first input terminal 304 of the comparator 302and Thres is also coupled to the second input terminal 306 of thecomparator 302.

The circuit of FIG. 12 may be used either for testing the pulser 300, asdescribed with reference to FIG. 7 , or for characterizing the CMUT 152,as described with reference to FIG. 9 . In operation, for testing thepulser 300, a control signal for the multiplexer 1205 (not illustratedin the figure) may control the multiplexer 1205 to select the voltage atthe first input terminal 1207 (i.e., at the node Sense) for outputtingat the output terminal 1111. Thus, the circuit may be equivalent to thecircuit of FIG. 7 . For characterizing the CMUT 152, the control signalfor the multiplexer 1205 (not illustrated in the figure) may control themultiplexer 1205 to select the voltage at the second input terminal 1209(i.e., the voltage at the node Thres) for outputting at the outputterminal 1211. Thus, the circuit may be equivalent to the circuit ofFIG. 9 .

For normal transmission of pulses using the pulser 300, the comparator302 may be capable of detecting crossings in both directions (e.g.,rising and falling) which may enable bipolar operation of the pulser300.

FIG. 13 is an example circuit diagram for further circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 13 is the same as FIG. 7 , except that FIG. 13 includes thechopper switch 1105 and the multiplexer 1205. The first input terminal1107 of the chopper switch 1105 is coupled to Sense, the second inputterminal 1109 is coupled to Thres, and the output terminal 1211 iscoupled to the positive input terminal 456 of the transconductanceamplifier 456. The first input terminal 1207 of the multiplexer 1205 iscoupled to Sense. The second input terminal 1209 is coupled to Thres.The output terminal 1211 is coupled to the positive input terminal 456of the transconductance amplifier 456. Further description of the use ofthe multiplexer 1205 for BIST may be found with reference to FIG. 12 .Further description of the use of the chopper switch 1105 forcontrolling polarity of the pulser 300 may be found with reference toFIG. 11 .

It should be appreciated from the foregoing discussion that thecircuitry illustrated in FIGS. 4-13 may be used both for built-inself-testing (BIST) of the pulser 300 and characterizing the CMUT 152.Table 1 summarizes configurations for built-in self-testing (BIST) ofthe pulser 300 and characterizing of the CMUT 152:

TABLE 1 Summary of configurations for testing the pulser 300 andcharacterizing the CMUT 152. Input voltage of Current transconductanceAmplifier 364 injected to Mode amplifier 454 Configuration amplifier 364Testing Pulser 300 V_(Sense) − V_(Thres0) Closed-Loop (TIA)$\frac{V_{Sense} - V_{{Thres}\; 0}}{n \cdot R_{s}}$ Characterizing CMUT152 V_(Thres) − V_(Thres0) Open-loop (Comparator)$\frac{V_{Thres} - V_{{Thres}\; 0}}{n \cdot R_{s}}$

FIG. 14 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 14 is a simplified version of FIG. 4 , except that FIG. 14includes receive circuitry 1484 instead of the receive circuitry 384.The receive circuitry 1484 (which may be an example of the receivecircuitry 184) is configurable as a delta-sigma analog-to-digitalconverter (ADC) 1400. Briefly, the delta-sigma ADC 1400 may beconsidered a second-order delta-sigma ADC that includes two feedbackloops. In operation, during normal imaging, the receive switch 162 maybe closed, and the delta-sigma ADC 1400 may integrate and then quantizecurrent output from the CMUT 152 to produce a digital logic level Dout.D_(OUT) may be a pulse stream in which the frequency of pulses may beproportional to the current inputted to the delta-sigma ADC 1400. Thisfrequency may be enforced by the feedback loops of the delta-sigma ADC1400.

The delta-sigma ADC 1400 includes a transconductance amplifier 1480, acapacitor 1492, a voltage quantizer 1420, a current digital-to-analogconverter (DAC) 1422, a current digital-to-analog converter (DAC) 1486,a switch 1487, and a switch 1421. The transconductance amplifier 1480has an input terminal 1482 and an output terminal 1484. The voltagequantizer 1420 has an input terminal 1428 and an output terminal 1432.The current DAC 1486 has an input terminal 1488 and an output terminal1490. The current DAC 1422 has an input terminal 1434 and an outputterminal 1436.

In the configuration of FIG. 14 , the input terminal 1482 of thetransconductance amplifier 1480, the output terminal 1436 of the currentDAC 1422, and the output terminal 460 of the transconductance amplifier454 are coupled together. (The output terminal 1436 of the current DAC1422 is coupled to this node through the closed switch 1421.) The outputterminal 1484 of the transconductance amplifier 1480, the outputterminal 1490 of the current DAC 1486, a terminal of the capacitor 1492,and the input terminal 1428 of the voltage quantizer 1420 are coupledtogether. (The output terminal 1490 of the current DAC 1486 is coupledto this node through the closed switch 1487.) The other terminal of thecapacitor 1492 is coupled to ground 1450. The output terminal 1432 ofthe voltage quantizer 1420, the input terminal 1488 of the current DAC1486, and the input terminal 1434 of the current DAC 1422 are coupledtogether. Further aspects of such delta-signal ADCs for convertingcurrent output of CMUTs are described in U.S. patent application Ser.No. 16/443,931 titled “APPARATUSES INCLUDING A CAPACITIVE MICROMACHINEDULTRASONIC TRANSDUCER DIRECTLY COUPLED TO AN ANALOG-TO-DIGITALCONVERTER,” filed on Jun. 18, 2019, and published on Oct. 3, 2019, asUS-2019-0299251-A1 (and assigned to the assignee of the instantapplication), which is incorporated by reference herein in its entirety.

FIG. 14 illustrates a non-limiting example of a configuration fortesting of the pulser 300. In operation, parasitic capacitance at thenode at the input terminal 1482 of the transconductance amplifier 1480may integrate the current output from the transconductance amplifier 454(which may be a transformed version of the HV output of the pulser 300)into a voltage prior to conversion of this voltage back into a currentby the transconductance amplifier 1480. The capacitor 1492 may integratethis current into a voltage that may then be quantized by the voltagequantizer 1420 to produce the digital output Dout. The output Dout ofthe delta-sigma ADC 1400 may be output by other circuitry in the receivecircuitry 1484 to an external device for analysis of the operation ofthe pulser 300. The capacitance at the node at the input terminal 1482of the transconductance amplifier 1480 may be lower than when the switch162 is closed and the capacitance of the CMUT 152 is added to theparasitic capacitance at this node. Thus, the stability and linearity ofthe delta-sigma ADC 1400 may be degraded. It may be helpful for thetransconductance amplifier 454's output current to be attenuated furtherto compensate for the loss in stability and linearity by reducing thesignal swing.

FIG. 15 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 15 is the same as FIG. 14 , with the following exceptions:

-   -   1. The positive input terminal of the transconductance amplifier        454 is coupled to Thres;    -   2. The switch 162 is closed;    -   3. The switch 1421 and the switch 1487 are open.

FIG. 15 illustrates a non-limiting example of a configuration forcharacterizing the CMUT 152 (e.g., characterizing its capacitance,collapse voltage, and/or stiction). In such a configuration, the pulser300 may be kept off, such that it does not output any high-voltagesignals. The voltage at Thres may be kept constant, such that thevoltage difference between Thres and Thres0 that is inputted to thetransconductance amplifier 454 is constant, and the output current fromthe transconductance amplifier 454 is constant. The constant currentoutput from the transconductance amplifier 454 may be integrated ontothe CMUT 152 to generate a ramp voltage at the input terminal 382 of thetransconductance amplifier 1480. The transconductance amplifier 1480 mayconvert this voltage to a current. The capacitor 1492 may integrate thiscurrent into a voltage. The quantizer 1420, operating as a comparator,may compare the ramp voltage to a reference voltage (referred to asVref, not illustrated). When the ramp voltage crosses Vref, the outputvoltage of the amplifier 364 may switch from high to low or from low tohigh. If the ramp begins at the voltage of an LV positive power supply(referred to as VDDA) and proceeds to ground 350, or if the ramp beginsat ground 350 and proceeds to VDDA, the configuration of FIG. 8 mayaccordingly be used to time how long it takes from the beginning of theramp to when the ramp cross Vref. The capacitance of the CMUT 152 may becomputed as

${C = \frac{I_{ramp} \times T_{ramp}}{{VDDA} - {Vref}}},$where I_(ramp) is the constant current outputted by the transconductanceamplifier 454 and T_(ramp) is the time it takes from the beginning ofthe ramp to when the ramp cross Vref. In some embodiments, two ramps maybe used, one during current sourcing and one during current sinking,such that one ramp proceeds from VDDA to ground 350 (during currentsinking) and one proceeds from ground 350 to VDDA (during currentsourcing), and the average of the T_(ramp) measured for each ramp may beused to compute C. In some embodiments, multiple repeated measurementsof the time for ramp voltages to cross the reference voltage may beperformed during current sourcing, and these multiple measurements oftime may be averaged. Additionally, multiple repeated measurements ofthe time for ramp voltages to cross the reference voltage may beperformed during current sinking, and these multiple measurements oftime may be averaged. The two averaged results, one result for currentsourcing and one for current sinking, may then be averaged together.Alternatively, the multiple measurements from current sourcing and fromcurrent sinking may be averaged together. It should be appreciated thatin some embodiments, measuring the time for a ramp voltage to cross thereference voltage during current sourcing may be performed prior tomeasuring the time for a ramp voltage to cross a reference voltageduring current sinking, while in some embodiments, measuring the timefor a ramp voltage to cross the reference voltage during current sinkingmay be performed prior to measuring the time for a ramp voltage to crossthe reference voltage during current sourcing.

In some embodiments, characterizing the CMUT 152 may includecharacterizing the collapse voltage of the CMUT 152. Characterizing thecollapse voltage of the CMUT 152 may include applying multiple differentbias voltage values V_(BIAS) to the CMUT 152. The bias voltage V_(BIAS)applied to the CMUT may be measured between the membrane of the CMUT 152and the bottom electrode at the substrate of the CMUT 152. If the bottomelectrode at the substrate of the CMUT 152 is at virtual ground, thenapplying V_(BIAS) to the CMUT may be accomplished by applying V_(BIAS)to the membrane. For each value of V_(BIAS), the capacitance of the CMUT152 may be computed as described above to produce a C vs. V_(BIAS)curve. A discontinuity may be detected in this curve when there iscontact between the membrane and the substrate of the CMUT 152. If the Cvs. V_(BIAS) curve was generated by increasing the value of V_(BIAS),then the value of V_(BIAS) at which this contact occurs (i.e., the valueof V_(BIAS) at which the discontinuity occurs) may be the collapsevoltage of the CMUT 152. A discontinuity may be detected in the C vs.V_(BIAS) curve by calculating the first and/or second derivative of thecurve.

In some embodiments, characterizing the CMUT 152 may includecharacterizing whether the membrane of the CMUT 152 is stuck to thesubstrate of the CMUT 152. A C vs. V_(BIAS) curve may be generated asdescribed above, and if no discontinuity is detected in the curve, thismay mean that the membrane of the CMUT 152 is stuck to the substrate ofthe CMUT 152. This may be because, for the entire range of V_(BIAS)values, the membrane is collapsed.

In some embodiments, applying V_(BIAS) to the membrane of the CMUT 152may include routing the voltage V_(BIAS) from circuitry in theultrasound device but external to the substrate on which the CMUT 152 isdisposed, through a routing network, and to the membrane of the CMUT152. It may be helpful to wait for the voltage at the membrane to settleto V_(BIAS) after charging or discharging the routing network.

In some embodiments, the transconductance amplifier 454 may be used(e.g., using the configuration of FIG. 4 or 14 ) to inject a waveform toreceive circuitry (e.g., the receive circuitry 384 or 1484 or any of theother receive circuitry described herein) for testing of the receivecircuitry. In operation, the pulser 300 may generate a multi-level pulsevoltage waveform (e.g., to mimic a sinewave test waveform), anattenuated version of this voltage waveform may be generated at Sense,the transconductance amplifier 454 may convert this voltage waveform toa current waveform and output this current waveform to the receivecircuitry. This may be an accurate and controllable method for injectinga test waveform to the receive circuitry. Additionally, when multipleblocks of circuitry include transconductance amplifiers 454, this methodmay allow for uniformity in generation of waveforms and testing based onthe waveforms across the different blocks.

FIG. 16A is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 16A is the same as FIG. 8 , except that the receive switch162 is closed, and FIG. 16A includes a current source 1685, a switch1686, a switch 1687, and a current source 1688 and lacks thetransconductance amplifier 454. The switch 1013 and the switch 1031 areopen, such that the amplifier 364 may operate as a comparator. (WhileFIG. 16A illustrates the receive circuitry 384, alternatively, thereceive circuitry 1484 may be used.) The current source 1685, which itshould be appreciated is distinct from the CMUT, is in series with theswitch 1686 and is coupled between a LV power supply 382 and thenegative input terminal 368 of the amplifier 364 (which is coupled,through the receive switch 162 to the node Out). The current source 1688is in series with the switch 1687 and is coupled between the negativeinput terminal 368 of the amplifier 364 and ground 350. The currentsource 1685 is couplable to the input terminal of the receive circuitry384 (in the example of FIG. 16A, to the negative input terminal 368 ofthe amplifier 364) by closing the switch 1686 and the current source1688 is couplable to the input terminal of the receive circuitry 384 byclosing the switch 1687. The current source 1685 may be configured tosupply current to the input terminal of the receive circuitry 384 andthe current source 1688 may be configured to sink current from the inputterminal of the receive circuitry 384.

The circuit of FIG. 16A may be used for characterizing the CMUT 152(e.g., characterizing its capacitance, collapse voltage, and/orstiction). In operation, the switch 1686 may be closed and the switch1687 may be opened, such that the current source 1685 supplies aconstant current to the node Out, charging or discharging the CMUT 152(depending on the polarity of its membrane voltage) and generating anincreasing ramp voltage at the node Out. Alternatively or additionally,the switch 1687 may be closed and the switch 1685 may be opened, suchthat the current source 1688 sinks a constant current from the node Out,charging or discharging the CMUT 152 (depending on the polarity of itsmembrane voltage) and generating a decreasing ramp voltage at the nodeOut. The amplifier 364, operating as a comparator, may compare the rampvoltage to the reference voltage (referred to as Vref) at the positiveinput terminal 366 of the amplifier 364. When the ramp voltage crossesVref, the output voltage of the amplifier 364 may switch from high tolow or from low to high. If the ramp begins at the voltage of the LVpositive power supply 1682 (referred to as VDDA) and proceeds to ground350 (i.e., the switch 1686 is closed), or if the ramp begins at ground350 and proceeds to VDDA (i.e., the switch 1687 is closed), theconfiguration of FIG. 16A may accordingly be used to measure the time ittakes from the beginning of the ramp to when the ramp cross Vref. Thecapacitance of the CMUT 152 may be computed as

${C = \frac{I_{ramp} \times T_{ramp}}{{VDDA} - {Vref}}},$where I_(ramp) is the constant current outputted by the current sources1685 and/or 1688, and T_(ramp) is the time it takes from the beginningof the ramp to when the ramp cross Vref. In some embodiments, two rampsmay be used, one during current sourcing and one during current sinking,such that one ramp proceeds from VDDA to ground 350 (during currentsinking) and one proceeds from ground 350 to VDDA (during currentsourcing), and the average of the T_(ramp) measured for each ramp may beused to compute C. In some embodiments, multiple repeated measurementsof the time for ramp voltages to cross the reference voltage may beperformed during current sourcing, and these multiple measurements oftime may be averaged. Additionally, multiple repeated measurements ofthe time for ramp voltages to cross the reference voltage may beperformed during current sinking, and these multiple measurements oftime may be averaged. The two averaged results, one result for currentsourcing and one for current sinking, may then be averaged together.Alternatively, the multiple measurements from current sourcing and fromcurrent sinking may be averaged together. It should be appreciated thatin some embodiments, measuring the time for a ramp voltage to cross thereference voltage during current sourcing may be performed prior tomeasuring the time for a ramp voltage to cross a reference voltageduring current sinking, while in some embodiments, measuring the timefor a ramp voltage to cross the reference voltage during current sinkingmay be performed prior to measuring the time for a ramp voltage to crossthe reference voltage during current sourcing.

In some embodiments, characterizing the CMUT 152 may includecharacterizing the collapse voltage of the CMUT 152. Characterizing thecollapse voltage of the CMUT 152 may include applying multiple differentbias voltage values V_(BIAS) to the CMUT 152. The bias voltage V_(BIAS)applied to the CMUT may be measured between the membrane of the CMUT 152and the bottom electrode at the substrate of the CMUT 152. If the bottomelectrode at the substrate of the CMUT 152 is at virtual ground, thenapplying V_(BIAS) to the CMUT may be accomplished by applying V_(BIAS)to the membrane. For each value of V_(BIAS), the capacitance of the CMUT152 may be computed as described above to produce a C vs. V_(BIAS)curve. A discontinuity may be detected in this curve when there iscontact between the membrane and the substrate of the CMUT 152. If the Cvs. V_(BIAS) curve was generated by increasing the value of V_(BIAS),then the value of V_(BIAS) at which this contact occurs (i.e., the valueof V_(BIAS) at which the discontinuity occurs) may be the collapsevoltage of the CMUT 152. A discontinuity may be detected in the C vs.V_(BIAS) curve by calculating the first and/or second derivative of thecurve.

In some embodiments, characterizing the CMUT 152 may includecharacterizing whether the membrane of the CMUT 152 is stuck to thesubstrate of the CMUT 152. A C vs. V_(BIAS) curve may be generated asdescribed above, and if no discontinuity is detected in the curve (e.g.,using a first and/or second derivative as described above), this maymean that the membrane of the CMUT 152 is stuck to the substrate of theCMUT 152. This may be because, for the entire range of V_(BIAS) values,the membrane is collapsed.

In some embodiments, applying V_(BIAS) to the membrane of the CMUT 152may include routing the voltage V_(BIAS) from circuitry in theultrasound device but external to the substrate on which the CMUT 152 isdisposed, through a routing network, and to the membrane of the CMUT152. It may be helpful to wait for the voltage at the membrane to settleto V_(BIAS) after charging or discharging the routing network.

FIG. 16B is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 16B is the same as FIG. 16A, except that the receive switch162 is open, the switch 1031 is closed such that the amplifier 364 maybe configured as a unity-gain voltage amplifier, the current sources1685 and 1688 are coupled through the switches 1686 and 1687,respectively, to the positive input terminal 366 of the amplifier 364,and a capacitor 1689 is coupled between the positive input terminal 366of the amplifier 364 and ground 350.

In some embodiments, the circuitry of FIG. 16B may be used to inject awaveform to the receive circuitry 384 for testing of the receivecircuitry 384. In operation, the switch 1686 may be closed and theswitch 1687 may be opened, such that the current source 1685 supplies aconstant current to the node Vp (i.e., the node at the positive inputterminal 366 of the amplifier 364), charging the capacitor 1689 andgenerating an increasing ramp voltage at the node Vp. Alternatively oradditionally, the switch 1687 may be closed and the switch 1686 may beopened, such that the current source 1688 sinks a constant current fromthe node Vp, discharging the capacitor 1689 and generating a decreasingramp voltage at the node Vp. This ramp voltage may be the waveforminjected to the receive circuitry 384 for testing the receive circuitry384.

FIG. 17 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 17 is the same as FIG. 3 , but with the addition of acapacitor network 1717 coupled between the pulser 300 and the receivecircuitry 384. (While FIGS. 17 and 21 illustrate the receive circuitry384, alternatively, the receive circuitry 1484 may be used.) Asdescribed above, it may be helpful to analyze the output of the pulser300 for testing purposes. While the receive circuitry 384 may be capableof converting analog voltages to digital codes and outputting thedigital codes to an external device where they can be analyzed, it maynot be feasible to directly connect the output of the pulser 300 to thereceive circuitry 384 (e.g., to the TIA 365). The output of the pulser300 may include pulses that are higher in voltage (e.g., in the HVdomain) than the operating voltage of the receive circuitry 384 (e.g.,in the LV domain). The inventors have recognized that, instead, thecapacitor network 1717 may be included between the pulser 300 and thereceive circuitry 384 for built-in self-testing (BIST). The capacitornetwork 1717 may be configured to convert the HV output of the pulser300 (or an attenuated version of the output of the pulser 300) to anattenuated voltage signal that can be processed and output by thereceive circuitry 384.

The capacitor network 1717 includes an input terminal 1719 and an outputterminal 1721. The input terminal 1719 of the capacitor network 1717 iscoupled to the Sense node. The output terminal 1721 of the capacitornetwork 1717 is coupled to the positive input terminal of the amplifier364. The switch 1031 is closed and the switch 1013 is open, such thatthe negative input terminal 368 of the amplifier 364 is coupled to theoutput terminal 370 of the amplifier 364. Thus, the amplifier 364 may beconfigured as a unity-gain voltage amplifier. In some embodiments, theremay be a voltage buffer between the capacitor network 1717 and thereceive circuitry 384.

The capacitor network 1717 may be used for built-in self-testing (BIST)of circuitry in the ultrasound system. FIG. 17 illustrates anon-limiting example of a configuration for testing of the pulser 300.In operation, the capacitor network 1717 may be configured to usecapacitive division to attenuate the voltage at Sense from the MV domainto the LV domain and to output the LV signal to the receive circuitry384. The capacitor divider consisting of the capacitor 346 and theparallel combination of the capacitor 348 and the input capacitance ofthe capacitor network 1717 may attenuate the HV signal at Out to the MVsignal at Sense, and the capacitor network 1717 may attenuate the MVsignal at Sense to a LV signal at the output terminal 1721. In someembodiments, the input capacitance of the capacitor network 1717 may besuch that when the voltage at Out is attenuated by the capacitor dividerconsisting of the capacitor 346 and the parallel combination of thecapacitor 348 and the input capacitance of the capacitor network 1717,then the attenuation ratio between the voltage at Out and the voltage atSense is as desired. For example, if the desired attenuation ratio isthat the voltage at Sense is 1/N the voltage at Out, then thecapacitance of the capacitor 346 may be C, the capacitance of thecapacitor 348 may be (N−1)C, and the input capacitance of the capacitornetwork 1717 may be C.

FIG. 18 is a circuit diagram of an example capacitor network 1817, inaccordance with certain embodiments described herein. The capacitornetwork 1817 may be used as the capacitor network 1717. The capacitornetwork 1817 may be configured to attenuate the voltage at Sense by 2 atthe node div 2, attenuate the voltage at div 2 by 2 at the node div 4,and attenuate the voltage at div 4 by 2 at div 8. The capacitor network1817 may therefore be configured to provide multiple attenuation optionswhich may be multiplexed to the output of the capacitor network 1817(which may be the same as the output terminal 1717 of the capacitornetwork 1717). The capacitor network 1817 also includes a node Commonthat may be at a constant voltage that can be coupled, through switches(not illustrated), to other nodes (e.g., div 2, div 4, and div 8) in thecapacitor network 1817, in order to reset the voltage across thecapacitors.

FIG. 19 is a circuit diagram of another example capacitor network 1917,in accordance with certain embodiments described herein. The capacitornetwork 1917 may be used as the capacitor network 1717. The capacitornetwork 1917 is the same as the capacitor network 1817, except that a 2Cand a C capacitor have been removed, such that the capacitor network maynot provide the div 8 attenuation option.

FIG. 20 is a circuit diagram of another example capacitor network 2017,in accordance with certain embodiments described herein. The capacitornetwork 2017 may be used as the capacitor network 1717. The capacitornetwork 2017 is the same as the capacitor network 1817, except that a 2Cand a C capacitor have been added, such that the capacitor networkprovides an output option for attenuation of div 8 by 2 at the node div16. It should be appreciated from FIGS. 18-20 that further or fewerattenuation options may be realized by adding or removing a 2C capacitorand a C capacitor in the manner illustrated.

FIG. 21 is an example schematic diagram illustrating circuitry in anultrasound system, in accordance with certain embodiments describedherein. FIG. 21 includes a pulser 2100 (which may be an example of thepulser 100), the capacitive micromachined ultrasonic transducer (CMUT)152, the receive switch 162, the receive circuitry 384, and a capacitornetwork 217. The capacitor network 2117 includes an input terminal 2119,a first output terminal 2121, and a second output terminal 2122. Theinput terminal 2119 of the capacitor network 2117 is coupled to the Outnode. The second output terminal 2122 of the capacitor network 2117 iscoupled to the positive input terminal of the amplifier 364. The firstoutput terminal 2121 of the capacitor network 2117 is coupled to thepositive input terminal 304 of the comparator 304. The switch 1031 isclosed and the switch 1013 is open, such that the negative inputterminal 368 of the amplifier 364 is coupled to the output terminal 370of the amplifier 364. Thus, the amplifier 364 may be connected as aunity-gain voltage amplifier.

The pulser 2100 is the same as the pulser 300, except that the pulser2100 lacks the capacitor 346 and the capacitor 348. Instead, theattenuation operation performed by the capacitor 346 and the capacitor348 in the pulser 300 may be performed by the capacitor network 2117. Inother words, the capacitor network 2117 may be configured to receive, asan input, an output signal from the pulser 2100 and output an attenuatedversion of the output signal from the pulser 2100 both to the pulser2100 and to the receive circuitry 384. In particular, in operation, thecapacitor network 2117 may receive the HV signal at Out at the inputterminal 2119 and output an attenuated, MV pulse signal at the firstoutput terminal 2121. In some embodiments, there may be a voltage bufferbetween the capacitor network 2117 and the receive circuitry 384.

The capacitor network 2117 may also be used for built-in self-testing(BIST) of circuitry in the ultrasound system. FIG. 21 illustrates anon-limiting example of a configuration for testing of the pulser 2100.In operation, the capacitor network 2117 may use capacitive division toattenuate the voltage at Out from the HV domain to the LV domain andoutput the LV signal to the receive circuitry 384.

FIG. 22 is a circuit diagram of an example capacitor network 2217, inaccordance with certain embodiments described herein. The capacitornetwork 2217 may be used as the capacitor network 2117. The capacitornetwork 2217 may be configured to only output at the node div 2 thepositive portion of the voltage at Sense such that the attenuation ratiofrom Out is 2. The capacitor network 2217 may be configured to output atthe node div 4 the voltage at div 2 attenuated by 2, to output at thenode div 8 the voltage at div 4 attenuated by 2, and to output at thenode divX the voltage at div 8 attenuated by a factor determined by acapacitor divider consisting of the capacitor coupled to the node divXand the load capacitance (Cload) of the circuit coupled to the node divX(e.g., at the second output terminal 2122). For example, the loadcapacitance may be input capacitance of the amplifier 364. In someembodiments, the attenuation ratio from div 8 to divX may beapproximately equal to C/Cload. In general, the attenuation ratios maydepend on Cload being much larger than C. The capacitor network 2217 maytherefore be configured to provide multiple attenuation options whichmay be multiplexed to the outputs of the capacitor network 1817 (whichmay be the same as the first output terminal 2121 and the second outputterminal 2122 of the capacitor network 1717). The voltage at div 4 anddiv 8 may be in the MV domain and may therefore be coupled to thepositive input terminal 304 of the comparator 302 (e.g., through thefirst output terminal 2121). The voltage at divX may be in LV domain andmay therefore be coupled to the positive input terminal of the amplifier364 (e.g., through the second output terminal 2122). The capacitornetwork 2217 may also include a node Common at a constant voltage thatcan be coupled, through switches (not illustrated), to other nodes(e.g., div 4, div 8, and divX) in the capacitor network 2217, in orderto reset the voltage across the capacitors. In some embodiments, thecapacitor network 2217 may require fewer units of capacitance than thecapacitor network 1817 in order to perform the same functions.

FIG. 23 is a circuit diagram of an example capacitor network 2317, inaccordance with certain embodiments described herein. The capacitornetwork 2317 may be used as the capacitor network 2117. The capacitornetwork 2317 is the same as the capacitor network 2217, except that a 2Cand a C capacitor have been removed. The capacitor network 2317 maytherefore provide at attenuation ratio of 2 at div 2, an attenuationratio of 4 at div 4, and an attenuation ratio approximately equal toC/Cload at divX.

FIG. 24 is a circuit diagram of another example capacitor network 2417,in accordance with certain embodiments described herein. The capacitornetwork 2417 may be used as the capacitor network 2117. The capacitornetwork 2417 is the same as the capacitor network 2217, except that a 2Cand a C capacitor have been added. The capacitor network 2217 may beconfigured to output at the node div 4 the voltage at div 2 attenuatedby 2, to output at the node div 8 the voltage at div 4 attenuated by 2,to output at the node div 16 the voltage at div 8 attenuated by 2, andto output at the node divX the voltage at div 16 attenuated by a factordetermined by a capacitor divider consisting of the capacitor coupled tothe node divX and the load capacitance (Cload) of the circuit coupled tothe node divX (e.g., at the second output terminal 2122). For example,the load capacitance may be input capacitance of the amplifier 364. Insome embodiments, the attenuation ratio from div 8 to divX may beapproximately equal to C/Cload. In general, the attenuation ratios maydepend on Cload being much larger than C. It should be appreciated fromFIGS. 22-24 that further or fewer attenuation options may be realized byadding or removing a 2C capacitor and a C capacitor in the mannerillustrated.

FIG. 25 is a circuit diagram of an example capacitor network 2517, inaccordance with certain embodiments described herein. The capacitornetwork 2517 may be used as the capacitor network 2117. The capacitornetwork 2517 may be configured to only output at the node div 2 thepositive portion of the voltage at Sense such that the attenuation ratiofrom Out is 2. The capacitor network 2517 may be configured to output atthe node div 4 the voltage at div 2 attenuated by 2, to output at thenode div 8 the voltage at div 4 attenuated by 2, and to output at thenode divX the voltage at div 8 attenuated by a factor determined by acapacitor divider consisting of the capacitor coupled to the node divXand the load capacitance (Cload) of the circuit coupled to the node divX(e.g., at the second input terminal 2122). For example, the loadcapacitance may be input capacitance of the amplifier 364. In someembodiments, the attenuation ratio from div 8 to divX may beapproximately equal to 2C/Cload. In general, the attenuation ratios maydepend on Cload being much larger than C. The capacitor network 2517 maytherefore be configured to provide multiple attenuation options whichmay be multiplexed to the outputs of the capacitor network 1817 (whichmay be the same as the first output terminal 2121 and the second outputterminal 2122 of the capacitor network 1717). The voltage at div 4 anddiv 8 may be in the MV domain and may therefore be coupled to thepositive input terminal 304 of the comparator 302 (e.g., through thefirst output terminal 2121). The voltage at divX may be in LV domain andmay therefore be coupled to the positive input terminal of the amplifier364 (e.g., through the second output terminal 2122). The capacitornetwork 2517 may also include a node Common at a constant voltage thatcan be coupled, through switches (not illustrated), to other nodes(e.g., div 4, div 8, and divX) in the capacitor network 2517, in orderto reset the voltage across the capacitors. In some embodiments, toremove an attenuation ratio from the capacitor network 2517, thecapacitor network 2317 may be used.

FIG. 26 is a circuit diagram of another example capacitor network 2617,in accordance with certain embodiments described herein. The capacitornetwork 2617 may be used as the capacitor network 2117. The capacitornetwork 2617 is the same as the capacitor network 2517, except that a 2Cand a C capacitor have been added. The capacitor network 2617 may beconfigured to output at the node div 4 the voltage at div 2 attenuatedby 2, to output at the node div 8 the voltage at div 4 attenuated by 2,to output at the node div 16 the voltage at div 8 attenuated by 2, andto output at the node divX the voltage at div 16 attenuated by a factordetermined by a capacitor divider consisting of the capacitor coupled tothe node divX and the load capacitance (Cload) of the circuit coupled tothe node divX (e.g., at the second output terminal 2122). For example,the load capacitance may be input capacitance of the amplifier 364. Insome embodiments, the attenuation ratio from div 8 to divX may beapproximately equal to 2C/Cload. It should be appreciated from FIGS.25-26 that further or fewer attenuation options may be realized byadding or removing a 2C capacitor and a C capacitor in the mannerillustrated. It should also be appreciated from FIGS. 22-26 that theattenuation ratio of the last stage may be modulated by modulating thecapacitor at the last stage. Depending of the attenuation ratios desiredand the voltage levels involved, one of the capacitor networks in FIGS.22-26 and a capacitance for the last stage may be selected.

FIGS. 27-34 illustrate ultrasound devices and substrates containingcircuitry that may be included in the ultrasound devices. As examples, asubstrate may include a semiconductor chip, a printed circuit board, amicroprocessor, or a field-programmable gate array (FPGA). It should beappreciated that, as illustrated in FIGS. 27-34 , any of the illustratedcircuitry may be integrated circuitry on a substrate (e.g., on asemiconductor chip). Thus, in some embodiments, BIST circuitry may beintegrated circuitry that is integrated on the same substrate (e.g., asemiconductor chip) as other integrated ultrasound circuitry such as apulsers and/or receive circuitry.

FIG. 27 is a block diagram of an ultrasound circuitry 2727, inaccordance with certain embodiments described herein. The ultrasoundcircuitry 2727 includes a substrate 2721. The substrate 2721 includesthe pulser 100, the CMUT 152, the receive circuitry 184, and a built-inself-test (BIST) circuit 2719. The BIST circuit 2719 may be thetransconductance amplifier 454, the capacitor network 1717, thecapacitor network 2117, the current source 1685, the current source1688, and/or the capacitor 1689. The output of the pulser 100 is coupledto the inputs of the CMUT 152 and the BIST circuit 2719. The output ofthe CMUT 152 is coupled to the input of the receive circuitry 184. Theoutput of the BIST circuit 2719 is coupled to the input of the receivecircuitry 184.

FIG. 28 is a block diagram of another example of ultrasound circuitry2827, in accordance with certain embodiments described herein. Theultrasound circuitry 2827 is the same as the ultrasound circuitry 2727,except that the ultrasound circuitry 2827 includes a substrate 2821 anda substrate 2823 instead of the substrate 2721. The pulser 100, the BISTcircuit 2719, and the receive circuitry 184 are disposed in thesubstrate 2821 and the CMUT 152 is disposed in the substrate 2823. Insome embodiments, the substrate 2821 and the substrate 2823 may bebonded together, and the CMUT 152 may be electrically coupled to thepulser 100 and the receive circuitry 184 through bonding points.

FIG. 29 is a block diagram of another example of ultrasound circuitry2927, in accordance with certain embodiments described herein. Theultrasound circuitry 2927 is the same as the ultrasound circuitry 2727,except that the ultrasound circuitry 2927 includes a substrate 2921 anda substrate 2925 instead of the substrate 2721. The pulser 100, the BISTcircuit 2719, and the CMUT 152 are disposed in the substrate 2921 andthe receive circuitry 184 is disposed in the substrate 2925. In someembodiments, the substrate 2921 and the substrate 2925 may be bondedtogether, and the receive circuitry 184 may be electrically coupled tothe BIST circuit 2719 and the CMUT 152 through bonding points.

FIG. 30 is a block diagram of another example of ultrasound circuitry3027, in accordance with certain embodiments described herein. Theultrasound circuitry 3027 is the same as the ultrasound circuitry 2927,except that the ultrasound circuitry 3027 includes a substrate 3021instead of the substrate 2921 and a substrate 3025 instead of thesubstrate 2925. The pulser 100 and the CMUT 152 are disposed in thesubstrate 3021 and the BIST circuit 2719 and the receive circuitry 184are disposed in the substrate 2925. In some embodiments, the substrate3021 and the substrate 3025 may be bonded together, and the pulser 100may be electrically coupled to the BIST circuit 2719 and the CMUT 152may be electrically coupled to the receive circuitry 184 through bondingpoints.

FIG. 31 is a block diagram of another example of ultrasound circuitry3127, in accordance with certain embodiments described herein. Theultrasound circuitry 3127 includes a substrate 3121 and a substrate3125. The substrate 3121 includes the pulser 100, the CMUT 152, the BISTcircuit 2719, receive circuitry 3129, and receive circuitry 3131. Thereceive circuitry 3129 and the receive circuitry 3131 may representdivision of the receive circuitry 184 into two blocks. The output of thepulser 100 is coupled to the inputs of the CMUT 152 and the BIST circuit2719. The output of the CMUT 152 is coupled to the input of the receivecircuitry 3129. The output of the BIST circuit 2719 is coupled to theinput of the receive circuitry 3129. The output of the receive circuitry3129 is coupled to the input of the receive circuitry 3131. In someembodiments, the substrate 3121 and the substrate 3125 may be bondedtogether, and the receive circuitry 3129 may be electrically coupled tothe receive circuitry 3131 through bonding points. In some embodiments,the substrate 3121 and the substrate 3125 may be electrically coupledthrough one or more communication links, and the receive circuitry 3129may be electrically coupled to the receive circuitry 3131 through thecommunication links. In some embodiments, the receive circuitry 3129 mayinclude a transimpedance amplifier and/or an analog-to-digital converter(ADC) and the receive circuitry 3131 may include digital processingcircuitry (although the receive circuitry 3129 and the receive circuitry3131 may include other circuitry as well). In some embodiments, thereceive circuitry 3129 may include a preamplifier, time-gaincompensation (TGC) circuitry, and/or analog beamforming circuitry, andthe receive circuitry 3131 may include a transimpedance amplifier, ananalog-to-digital converter (ADC), and/or digital processing circuitry(although the receive circuitry 3129 and the receive circuitry 3131 mayinclude other circuitry as well).

FIG. 32 is a block diagram of another example of ultrasound circuitry3227, in accordance with certain embodiments described herein. Theultrasound circuitry 3227 includes a substrate 3221, the substrate 2823,and the substrate 2925. The pulser 100 and the BIST circuit 2719 aredisposed in the substrate 3221. In some embodiments, the substrate 3221and the substrate 2823 may be bonded together, and the substrate 3221and the substrate 2925 may be bonded together. In such embodiments, theCMUT 152 may be electrically coupled to the pulser 100 and the receivecircuitry 184 through bonding points.

FIG. 33 is a block diagram of another example of ultrasound circuitry3327, in accordance with certain embodiments described herein. Theultrasound circuitry 3327 includes a substrate 3321, the substrate 2823,and the substrate 3325. The pulser 100 is disposed in the substrate AF21and the BIST circuit 2719 and the receive circuitry 184 are disposed inthe substrate 3325. In some embodiments, the substrate 3321 and thesubstrate 2823 may be bonded together, and the substrate 33V21 and thesubstrate 3325 may be bonded together. In such embodiments, the CMUT 152may be electrically coupled to the pulser 100 and the receive circuitry184 through bonding points, and the pulser 100 may be electricallycoupled to the BIST circuit 2719 through bonding points.

FIG. 34 is a block diagram of another example of ultrasound circuitry3427, in accordance with certain embodiments described herein. Theultrasound circuitry 3427 includes a substrate 3421, the substrate 2823,and the substrate 3125. The pulser 100, the BIST circuit 2719, and thereceive circuitry 3129 are disposed in the substrate 3421. In someembodiments, the substrate 3421 and the substrate 2823 may be bondedtogether, and the CMUT 152 may be electrically coupled to the pulser 100and the receive circuitry 3129 through bonding points. In someembodiments, the substrate 3421 and the substrate 3125 may be bondedtogether, and the receive circuitry 3129 may be electrically coupled tothe receive circuitry 3131 through bonding points. In some embodiments,the substrate 3421 and the substrate 3125 may be electrically coupledthrough one or more communication links, and the receive circuitry 3129may be electrically coupled to the receive circuitry 3131 through thecommunication links.

In any of the substrates described herein, the pulser 100, the BISTcircuit 2719, the receive circuitry 184, the receive circuitry 3129,and/or the receive circuitry 3131 may be integrated circuitry fabricatedin the substrate (e.g., in a semiconductor chip). Additionally, in anyof the substrates described herein that include such integratedcircuitry and the CMUT 152, the CMUT 152 may be fabricated in thesubstrate after the integrated circuitry has been fabricated in thesubstrate.

It should be appreciated that in any of the ultrasound devices describedherein that include two or more substrates, any or all of the substratesmay be included in a single package. Thus, the BIST circuit 2719, thereceive circuitry, CMUT 152, and the pulser 100 may be disposed within asingle package. The BIST circuit 2719 may thus be included in the finalultrasound device product, despite potentially not being used once theultrasound device is in the hands of consumers.

FIG. 35A illustrates a flow diagram for a process 3500A for testing apulser in an ultrasound device, in accordance with certain embodimentsdescribed herein. The process 3500A may be performed by operating atransconductance amplifier (e.g., the transconductance amplifier 454)coupled between a pulser (e.g., the pulser 300) and receive circuitry(e.g., the receive circuitry 184, the receive circuitry 384, or thereceive circuitry 1484) in an ultrasound device (e.g., the ultrasounddevice 4402 described below).

In act 3502A, the transconductance amplifier is operated to convert avoltage outputted by the pulser in the ultrasound device to a current.The process 3500A proceeds from act 3502A to act 3504A.

In act 3504A, the transconductance amplifier is operated to output thecurrent to the receive circuitry (e.g., to a TIA (e.g., the TIA 365) orto a delta-sigma ADC (e.g., the delta-sigma ADC 1400) in the receivecircuitry) in the ultrasound device. In some embodiments, after testingthe pulser, the transconductance amplifier may be shut off while thepulser and the receive circuitry remain on. Further description ofcircuitry that may be configured to perform the process 3500A may befound with reference to FIGS. 4-7 and 10-14 . The process 3500A may alsobe used for testing the receive circuitry as described after thedescription of FIG. 15 .

FIG. 35B illustrates a flow diagram for a process 3500B for testingreceive circuitry (e.g., the receive circuitry 384) in an ultrasounddevice, in accordance with certain embodiments described herein. Theprocess 3500B may be performed by operating current sources (e.g., thecurrent sources 1685 and 1688) each coupled through a switch (e.g., theswitches 1686 and 1687) to a capacitor (e.g., the capacitor 1689) and toan input terminal of the receive circuitry (i.e., the positive inputterminal 366 of the amplifier 364).

In act 3502B, the current sources and switches are operated to generatea current. For example, one of the switches may be closed and the otherswitch may be opened, such that one of the current sources supplies aconstant current to the capacitor and charges the capacitor, generatingan increasing ramp voltage at the input terminal of the receivecircuitry. Alternatively or additionally, the switch may be opened andthe other switch may be closed, such that the other current sourcessupplies a constant current to the capacitor and discharges thecapacitor, generating an decreasing ramp voltage at the input terminalof the receive circuitry.

In act 3504B, the ramp voltage generated in act 3502B is output to thereceive circuitry (e.g., to an amplifier (e.g., the amplifier 364)configured as a unity-gain buffer) in the ultrasound device. This rampvoltage may be the waveform injected to the receive circuitry 384 fortesting the receive circuitry 384.

FIG. 36 illustrates a flow diagram for a process 3600 for testing apulser in an ultrasound device, in accordance with certain embodimentsdescribed herein. The process 3600 may be performed by operating acapacitor network (e.g., the capacitor network 1717 or the capacitornetwork 2117) coupled between a pulser (e.g., the pulser 300 or thepulser 2100) and receive circuitry (e.g., the receive circuitry 184, thereceive circuitry 384, or the receive circuitry 1484) in an ultrasounddevice (e.g., the ultrasound device 4402 described below).

In act 3602, the capacitor network is operated to attenuate a voltageoutputted by the pulser in the ultrasound device. The process 3600proceeds from act 3602 to act 3604.

In act 3604, the capacitor network is operated to output the attenuatedvoltage to the receive circuitry (e.g., to a unity-gain amplifier in thereceive circuitry) in the ultrasound device. In some embodiments, thecapacitor network may also output an attenuated version of the output ofthe pulser back to the pulser itself. Further description of circuitrythat may be configured to perform the process 3600 may be found withreference to FIGS. 17-26 .

FIG. 37 illustrates a flow diagram for a process 3700 for characterizinga capacitive micromachined ultrasonic transducer (CMUT) (e.g., the CMUT352), in accordance with certain embodiments described herein. Forexample, the characterization may be characterization of the CMUT'scapacitance. The process 3700 may be performed by operating atransconductance amplifier (e.g., the transconductance amplifier 454)coupled to receive circuitry (e.g., the receive circuitry 184, thereceive circuitry 384, or the receive circuitry 1484) in an ultrasounddevice (e.g., the ultrasound device 4402 described below). An inputterminal of the receive circuitry is electrically coupled to the CMUT.For example, to electrically couple the CMUT to the input terminal ofthe receive circuitry, a switch (e.g., the receive switch 362) betweenthe CMUT and the input terminal of the receive circuitry may be closed.

In act 3702, the transconductance amplifier is operated to generate acurrent. For example, the transconductance amplifier may accept constantvoltages at its inputs and output a constant current based on thedifference between the two inputted voltages. The process 3700 proceedsfrom act 3702 to act 3704.

In act 3704, the transconductance amplifier is operated to inject thecurrent to the input terminal of the receive circuitry (e.g., to anamplifier configured as a comparator). The current may charge ordischarge the CMUT to generate a ramp voltage. The ramp may begin at thevoltage VDDA of a positive power supply and proceed to ground or beginat ground and proceed to VDDA. The receive circuitry (e.g., a comparatorin the receive circuitry) may be used to measure the time T_(ramp) ittakes for the ramp voltage to cross a reference voltage Vref. Thecapacitance of the CMUT may be computed as

${C = \frac{I_{ramp} \times T_{ramp}}{{VDDA} - {Vref}}},$where T_(ramp) is the constant current generated by the transconductanceamplifier and T_(ramp) is the time it takes from the beginning of theramp to when the ramp cross the reference voltage Vref. In someembodiments, after characterizing the CMUT, the transconductanceamplifier may be shut off while the pulser and the receive circuitryremain on. Further description of circuitry that may be configured toperform the process 3700 may be found with reference to FIGS. 8-13 and15 .

In some embodiments, the same transconductance amplifier coupled betweenthe pulser and the receive circuitry may be used to test the pulser andto characterize the CMUT in the ultrasound device. FIG. 38 illustrates aflow diagram for a process 3800 for testing a pulser in an ultrasounddevice, in accordance with certain embodiments described herein. Theprocess 3800 may be performed by operating a transconductance amplifier(e.g., the transconductance amplifier 454) coupled between a pulser(e.g., the pulser 300) and receive circuitry (e.g., the receivecircuitry 184, the receive circuitry 384, or the receive circuitry 1484)in an ultrasound device (e.g., the ultrasound device 4402 describedbelow).

In act 3802, the transconductance amplifier is operated to convert afirst voltage outputted by the pulser in the ultrasound device to afirst current. The process 3800 proceeds from act 3802 to act 3804.

In act 3804, the transconductance amplifier is operated to output thefirst current to the receive circuitry (e.g., to an amplifier configuredas a TIA (e.g., the TIA 365) in the receive circuitry) in the ultrasounddevice. Further description of circuitry that may be configured toperform the acts 3802-3804 may be found with reference to FIGS. 4-7 and10-14 .

In act 3806, the transconductance amplifier is operated to generate asecond current. For example, the transconductance amplifier may acceptconstant voltages at its inputs and output a constant current based onthe difference between the two inputted voltages. The process 3800proceeds from act 3806 to act 3808.

In act 3808, the transconductance amplifier is operated to inject thesecond current to an input terminal of the receive circuitry (e.g., toan amplifier (e.g., the amplifier 364) configured as a comparator). Theinput terminal of the receive circuitry is electrically coupled to theCMUT. For example, to electrically couple the CMUT to the input terminalof the receive circuitry, a switch (e.g., the receive switch 362)between the CMUT and the input terminal of the receive circuitry may beclosed. The second current may charge or discharge the CMUT to generatea ramp voltage. The ramp may begin at the voltage VDDA of a positivepower supply and proceed to ground or begin at ground and proceed toVDDA. The receive circuitry (e.g., a comparator in the receivecircuitry) may be used to measure the time T_(ramp) it takes for theramp voltage to cross a reference voltage Vref. The capacitance of theCMUT may be computed as

${C = \frac{I_{ramp} \times T_{ramp}}{{VDDA} - {Vref}}},$where I_(ramp) is the constant current generated by the transconductanceamplifier and T_(ramp) is the time it takes from the beginning of theramp to when the ramp cross the reference voltage Vref. Furtherdescription of circuitry that may be configured to perform the acts3806-3808 may be found with reference to FIGS. 8-13 and 15 . In someembodiments, acts 3806-3808 may be performed before acts 3802-3804.

In some embodiments, a process for characterizing a CMUT (e.g., the CMUT352) may include operating a current source (e.g., the current source1685 or 1688) in the ultrasound device to inject a current to an inputterminal of receive circuitry (e.g., to an amplifier (e.g., theamplifier 364) configured as a comparator). The input terminal iselectrically coupled to the CMUT. For example, to electrically couplethe CMUT to the input terminal of the receive circuitry, a switch (e.g.,the receive switch 362) between the CMUT and the input terminal of thereceive circuitry may be closed. The current may charge or discharge theCMUT to generate a ramp voltage. The ramp may begin at the voltage VDDAof a positive power supply and proceed to ground or begin at ground andproceed to VDDA. The receive circuitry (e.g., a comparator in thereceive circuitry) may be used to measure the time T_(ramp) it takes forthe ramp voltage to cross a reference voltage Vref. The capacitance ofthe CMUT may be computed as

${C = \frac{I_{ramp} \times T_{ramp}}{{VDDA} - {Vref}}},$where I_(ramp) is the constant current generated by the transconductanceamplifier and T_(ramp) is the time it takes from the beginning of theramp to when the ramp cross the reference voltage Vref. In someembodiments, one current source may source a first current to the inputterminal of the receive circuitry to charge or discharge the CMUT andgenerate a first ramp voltage. A first time for the first ramp voltageto cross a reference voltage may be measured. A second current sourcemay sink a second current from the input terminal of the receivecircuitry to charge or discharge the CMUT and generate a second rampvoltage. A second time for the second ramp voltage to cross thereference voltage may be measured. Both the first and second time may beused to compute the capacitance (e.g., by averaging the first and secondtimes and using the above equation). In some embodiments, multiplerepeated measurements of the time for ramp voltages to cross thereference voltage may be performed during current sourcing, and thesemultiple measurements of time may be averaged. Additionally, multiplerepeated measurements of the time for ramp voltages to cross thereference voltage may be performed during current sinking, and thesemultiple measurements of time may be averaged. The two averaged results,one result for current sourcing and one for current sinking, may then beaveraged together. Alternatively, the multiple measurements from currentsourcing and from current sinking may be averaged together. It should beappreciated that in some embodiments, measuring the time for a rampvoltage to cross the reference voltage during current sourcing may beperformed prior to measuring the time for a ramp voltage to cross areference voltage during current sinking, while in some embodiments,measuring the time for a ramp voltage to cross the reference voltageduring current sinking may be performed prior to measuring the time fora ramp voltage to cross the reference voltage during current sourcing.Further description of circuitry that may be configured to perform sucha process may be found with reference to FIG. 16A.

FIG. 39 illustrates a process 3900 for performing measurements in orderto determine the collapse voltage of a CMUT (e.g., the CMUT 152), inaccordance with certain embodiments described herein. The process 3900may be performed by an ultrasound device (e.g., the ultrasound device4402 described below).

In act 3902, the ultrasound device applies a bias voltage V_(BIAS) to aCMUT. The bias voltage V_(BIAS) applied to the CMUT may be measuredbetween the membrane of the CMUT and the bottom electrode at thesubstrate of the CMUT. If the bottom electrode at the substrate of theCMUT is at virtual ground, then applying V_(BIAS) to the CMUT may beaccomplished by applying V_(BIAS) to the membrane. In some embodiments,the ultrasound device may use a DC-DC converter (e.g., the DC-DCconverter 4339 described below) to apply the bias voltage V_(BIAS) tothe membrane of the CMUT.

In some embodiments, applying V_(BIAS) to the membrane of the CMUT mayinclude routing the voltage V_(BIAS) from circuitry (e.g., the DC-DCconverter 4339 described below) in the ultrasound device but external tothe substrate on which the CMUT is disposed, through a routing network,and to the membrane of the CMUT. It may be helpful to wait for thevoltage at the membrane to settle to V_(BIAS) after charging ordischarging the routing network.

In act 3904, the ultrasound device measures a capacitance or a parameterrelated to the capacitance of the CMUT at the bias voltage applied inact 3902. In some embodiments, the ultrasound device may perform act3904 by operating a transconductance amplifier (e.g., thetransconductance amplifier 454) coupled to receive circuitry (e.g., thereceive circuitry 184, the receive circuitry 384, or the receivecircuitry 1484) in the ultrasound device. An input terminal of thereceive circuitry is electrically coupled to the CMUT. For example, toelectrically couple the CMUT to the input terminal of the receivecircuitry, a switch (e.g., the receive switch 362) between the CMUT andthe input terminal of the receive circuitry may be closed. Thetransconductance amplifier may be operated to generate a current. Forexample, the transconductance amplifier may accept constant voltages atits inputs and output a constant current I_(ramp) based on thedifference between the two inputted voltages. The transconductanceamplifier may be operated to inject the current to the input terminal ofthe receive circuitry (e.g., to an amplifier configured as acomparator). The current may charge or discharge the CMUT to generate aramp voltage. If the ramp begins at the voltage of an LV positive powersupply (referred to as VDDA) and proceeds to ground, or if the rampbegins at ground and proceeds to VDDA, the ultrasound device may use thereceive circuitry (e.g., a comparator in the receive circuitry) tomeasure the time T_(ramp) that it takes from the beginning of the rampto when the ramp crosses a reference voltage Vref. In some embodiments,two ramps may be used, one during current sourcing and one duringcurrent sinking, such that one ramp proceeds from VDDA to ground (duringcurrent sinking) and one proceeds from ground to VDDA (during currentsourcing), and the average of the T_(ramp) measured for each ramp may beused to compute C. In some embodiments, multiple repeated measurementsof the time for ramp voltages to cross the reference voltage may beperformed during current sourcing, and these multiple measurements oftime may be averaged. Additionally, multiple repeated measurements ofthe time for ramp voltages to cross the reference voltage may beperformed during current sinking, and these multiple measurements oftime may be averaged. The two averaged results, one result for currentsourcing and one for current sinking, may then be averaged together.Alternatively, the multiple measurements from current sourcing and fromcurrent sinking may be averaged together. It should be appreciated thatin some embodiments, measuring the time for a ramp voltage to cross thereference voltage during current sourcing may be performed prior tomeasuring the time for a ramp voltage to cross a reference voltageduring current sinking, while in some embodiments, measuring the timefor a ramp voltage to cross the reference voltage during current sinkingmay be performed prior to measuring the time for a ramp voltage to crossthe reference voltage during current sourcing.

In some embodiments, the ultrasound device may operate a current source(e.g., the current source 1685 or 1688) to inject a current to an inputterminal of receive circuitry (e.g., to an amplifier (e.g., theamplifier 364) configured as a comparator). The input terminal iselectrically coupled to the CMUT. For example, to electrically couplethe CMUT to the input terminal of the receive circuitry, a switch (e.g.,the receive switch 362) between the CMUT and the input terminal of thereceive circuitry may be closed. The current may charge or discharge theCMUT to generate a ramp voltage. The receive circuitry (e.g., acomparator in the receive circuitry) may be used to measure the timeT_(ramp) it takes for the ramp voltage to cross a reference voltageVref. In some embodiments, one current source may source a first currentto the input terminal of the receive circuitry to charge or dischargethe CMUT and generate a first ramp voltage. A first time T_(ramp) forthe first ramp voltage to cross a reference voltage may be measured. Asecond current source may sink a second current from the input terminalof the receive circuitry to charge or discharge the CMUT and generate asecond ramp voltage. A second time T_(ramp) for the second ramp voltageto cross the reference voltage may be measured. Both the first andsecond times T_(ramp) may be used to compute the capacitance (e.g., byaveraging the T_(ramp) values). In some embodiments, multiple repeatedmeasurements of the time for ramp voltages to cross the referencevoltage may be performed during current sourcing, and these multiplemeasurements of time may be averaged. Additionally, multiple repeatedmeasurements of the time for ramp voltages to cross the referencevoltage may be performed during current sinking, and these multiplemeasurements of time may be averaged. The two averaged results, oneresult for current sourcing and one for current sinking, may then beaveraged together. Alternatively, the multiple measurements from currentsourcing and from current sinking may be averaged together. It should beappreciated that in some embodiments, measuring the time for a rampvoltage to cross the reference voltage during current sourcing may beperformed prior to measuring the time for a ramp voltage to cross areference voltage during current sinking, while in some embodiments,measuring the time for a ramp voltage to cross the reference voltageduring current sinking may be performed prior to measuring the time fora ramp voltage to cross the reference voltage during current sourcing.

The capacitance of the CMUT may be computed based on T_(ramp) as

$C = {\frac{I_{ramp} \times T_{ramp}}{{VDDA} - {Vref}}.}$In some embodiments, the ultrasound device may measure T_(ramp) but notuse T_(ramp) to measure C. In some embodiments, the ultrasound deviceitself may use T_(ramp) to measure C. Further description of circuitrythat may be configured to perform the act 3904 may be found withreference to FIGS. 8-13 and 15-16 .

The ultrasound device may repeat acts 3902 and 3904 by choosing a newbias voltage V_(BIAS) to apply to the CMUT at act 3902 and repeating themeasurement at the new bias voltage at act 3904. In some embodiments,the ultrasound device may use increasing values of the bias voltage. Atact 3906, if there is an additional bias voltage to apply, theultrasound device returns back to act 3902 and applies the new biasvoltage. If there is not an additional bias voltage to apply, theprocess 3900 terminates.

In some embodiments, the values of the capacitance C of the CMUT or thevalues of the parameter (e.g., T_(ramp)) related to the capacitance ofthe CMUT at each of the bias voltages V_(BIAS) may represent a C vs.V_(BIAS) curve. In some embodiments, the ultrasound device may transmitthe measurements of the capacitance or of the parameter (e.g., T_(ramp))related to the capacitance of the CMUT to a processing device (e.g., theprocessing device 4404 described below) which is in operativecommunication with the ultrasound device. For example, the ultrasounddevice may transmit the processing device over a wired communicationlink (e.g., over Ethernet, a Universal Serial Bus (USB) cable or aLightning cable) or over a wireless communication link (e.g., over aBLUETOOTH, WiFi, or ZIGBEE wireless communication.

FIG. 40 illustrates a process 4000 for determining the collapse voltagesof one or more CMUTs (e.g., one of which may be the CMUT 152) andapplying a bias voltage to the CMUTs, in accordance with certainembodiments described herein. The process 4000 may be performed by aprocessing device (e.g., the processing device 4404 described below).The processing device may be in operative communication with anultrasound device (e.g., the ultrasound device 4402 described below).For example, the processing device may be a mobile phone, tablet, orlaptop. The ultrasound device and the processing device may communicateover a wired communication link (e.g., over Ethernet, a Universal SerialBus (USB) cable or a Lightning cable) or over a wireless communicationlink (e.g., over a BLUETOOTH, WiFi, or ZIGBEE wireless communicationlink). In some embodiments, the process 4000 may be performed by theultrasound device.

In act 4002, the processing device receive sets of measurements ofcapacitances or a parameter related to the capacitances of one or moreCMUTs at each of multiple bias voltages applied to the CMUTs. Furtherdescription of such measurements may be found above with reference tothe process 3900. As described above, the ultrasound device may measureT_(ramp), which can be used to compute C. In some embodiments, for eachof the multiple CMUTs, the processing device may receive a set ofmeasurements of T_(ramp) at multiple bias voltages. In some embodiments,the set of measurements of T_(ramp) may have been collected atincreasing bias voltages. In some embodiments, for each of the multipleCMUTs, the processing device may receive a set of measurements of C atmultiple increasing bias voltages. The ultrasound device may transmitthe sets of measurements to the processing device over a wiredcommunication link (e.g., over Ethernet, a Universal Serial Bus (USB)cable or a Lightning cable) or over a wireless communication link (e.g.,over a BLUETOOTH, WiFi, or ZIGBEE wireless communication. In someembodiments, the multiple CMUTs may be all the CMUTs in a CMUT array onthe ultrasound device. In some embodiments, the multiple CMUTs may be asubset of the CMUTs in a CMUT array on the ultrasound device.

In act 4004, the processing device determines collapse voltages of theone or more CMUTs based on the capacitances of the CMUTs at each of themultiple bias voltages received in act 4002. In embodiments in which theprocessing device receives sets of measurements of T_(ramp) at multiplebias voltages, the processing device may compute C at each of the biasvoltages for each CMUT using the equation

${C = \frac{I_{ramp} \times T_{ramp}}{{VDDA} - {Vref}}},$where I_(ramp) is the constant current inputted to the CMUT thatgenerates the ramp voltage from ground to the voltage of the positivepower supply VDDA or from VDDA to ground and T_(ramp) is the time ittakes from the beginning of the ramp to when the ramp cross thereference voltage Vref. As described above, in some embodiments, theultrasound device may measure multiple values for T_(ramp) at a singlebias voltage for each CMUT; for example, the ultrasound device maymeasure one value for an increasing ramp voltage and another value for adecreasing ramp voltage. In such embodiments, the processing device mayaverage the multiple values of T_(ramp) and use the averaged value tocompute C for each CMUT.

The measurements of C at each of the bias voltages V_(BIAS) mayconstitute a C vs. V_(BIAS) curve for each CMUT. A discontinuity may beobserved in this curve when there is contact between the membrane andthe substrate of the CMUT. If the C vs. V_(BIAS) curve was generated byincreasing the value of V_(BIAS), then the value of V_(BIAS) at whichthis contact occurs (i.e., the value of V_(BIAS) at which thediscontinuity occurs) may be the collapse voltage of the CMUT 152. Theprocessing device may thus determine the collapse voltage of each CMUTby computing the first or second derivative of the C vs. V_(BIAS) curveand determining where a discontinuity occurs in the curve. Theprocessing device may calculate the first and/or second derivative ofthe C vs. V_(BIAS) curve in order to determine where the discontinuityoccurs.

In act 4006, the processing device causes a bias voltage to be appliedto the one or more CMUTs based at least in part on the collapse voltagesof the one or more CMUTs. The bias voltage applied to the CMUT may bemeasured between the membranes of the CMUTs and the bottom electrodes atthe substrates of the CMUTs. If the desired bias voltage is V_(BIAS),and the bottom electrodes at the substrates of the CMUTs are at virtualground, then applying V_(BIAS) to the CMUT may be accomplished byapplying V_(BIAS) to the membrane. In some embodiments, the processingdevice may compute the average of the collapse voltages of the CMUTsthat were computed in act 4004 and cause a bias voltage to be applied tothe CMUTs that is greater than the average of the collapse voltages by aparticular offset voltage. Thus, the same bias voltage may be applied toeach of the CMUTs. In some embodiments in which the same bias voltage isapplied to each of the CMUTs, each of the CMUTs may share one membrane.Alternatively, the processing device may cause different bias voltagesto be applied to different CMUTs. For example, if one group of CMUTsshares one membrane and another group of CMUTs shares another membrane,then the processing device may calculate the average collapse voltagefor each group and cause a bias voltage to be applied to each group thatis greater than that group's average collapse voltage by the particularoffset voltage. As another example, if each CMUT has its own membrane,the processing device may cause a bias voltage to be applied to eachCMUT that is greater than that CMUT's collapse voltage by the particularoffset voltage. In some embodiments, when computing the average of thecollapse voltages of multiple CMUTs, the processing device may excludefrom the computation those CMUTs having membranes that are stuck totheir substrates. The processing device may determine which CMUTs arestuck based on determining that the CMUTs' C vs. V_(BIAS) curves do nothave discontinuities.

In some embodiments, the offset voltage may be approximately equal to orbetween 20-30V. For example, the offset voltage may be approximatelyequal to 25, 26, 27, 28, 29, or 30V. In some embodiments, the offsetvoltage may be approximately equal to or between 20-45V. For example,the offset voltage may be approximately equal to 20, 21, 22, 23, 24, 25,26, 27, 28, 29, 30, 31, 32, 33, 34, or 35V. However, other suitableoffset voltages may be used. In some embodiments, a different offsetvoltage may be used when imaging different anatomical regions. Forexample, different presets (i.e., where each preset is a predeterminedset of imaging parameters optimized for imaging a particular anatomicalregion) may use different offset voltages. Applying a bias voltage tothe CMUTs that is a particular offset voltage greater than the averageof the collapse voltages of the CMUTs may help to ensure that, as thecollapse voltages of the CMUTs change with time, the value of the biasvoltage applied to the CMUTs minus the average of the collapse voltagesof the CMUTs remains the same. This may help to increase the acousticefficiency of the CMUT. The processing device may transmit aninstruction to the ultrasound device to apply the bias voltage over awired communication link (e.g., over Ethernet, a Universal Serial Bus(USB) cable or a Lightning cable) or over a wireless communication link(e.g., over a BLUETOOTH, WiFi, or ZIGBEE wireless communication. In someembodiments, the ultrasound device may use a DC-DC converter (e.g., theDC-DC converter 4339 described below) to apply the bias voltage V_(BIAS)to the membrane of the CMUT.

FIG. 41 illustrates a process 4100 for generating a notification basedon measurements of capacitance of CMUTs (e.g., one of which may be theCMUT 152), in accordance with certain embodiments described herein. Theprocess 4100 may be performed by a processing device (e.g., theprocessing device 4404 described below). The processing device may be inoperative communication with an ultrasound device (e.g., the ultrasounddevice 4402 described below). For example, the processing device may bea mobile phone, tablet, or laptop. The ultrasound device and theprocessing device may communicate over a wired communication link (e.g.,over Ethernet, a Universal Serial Bus (USB) cable or a Lightning cable)or over a wireless communication link (e.g., over a BLUETOOTH, WiFi, orZIGBEE wireless communication link). In some embodiments, the process4100 may be performed by the ultrasound device.

In act 4102, the processing device receive sets of measurements ofcapacitance or a parameter related to the capacitance of multiple CMUTsat each of multiple bias voltages applied to the multiple CMUTs. The act4102 is the same as the act 4002. In some embodiments, the multipleCMUTs may be all the CMUTs in a CMUT array on the ultrasound device. Insome embodiments, the multiple CMUTs may be a subset of the CMUTs in aCMUT array on the ultrasound device. As described above, in someembodiments, the ultrasound device may measure T_(ramp), which can beused to compute C, the capacitance of a CMUT at a given bias voltage. Insome embodiments, at act 4102, the processing device may receive a setof measurements of T_(ramp) at multiple bias voltages for each of themultiple CMUTs. In some embodiments, at act 4102, the processing devicemay receive a set of measurements of C at multiple bias voltages foreach of the multiple CMUTs.

In embodiments in which the processing device receives sets ofmeasurements of T_(ramp) at multiple bias voltages, the processingdevice may compute C at each of the bias voltages for each CMUT usingthe equation

${C = \frac{I_{ramp} \times T_{ramp}}{{VDDA} - {Vref}}},$where I_(ramp) is the constant current inputted to the CMUT thatgenerates the ramp voltage from ground to the voltage of the positivepower supply VDDA or from VDDA to ground and T_(ramp) is the time ittakes from the beginning of the ramp to when the ramp cross thereference voltage Vref. As described above, in some embodiments, theultrasound device may measure multiple values for T_(ramp) at a singlebias voltage for each CMUT; for example, the ultrasound device maymeasure one value for an increasing ramp voltage and another value for adecreasing ramp voltage. In such embodiments, the processing device mayaverage the multiple values of T_(ramp) and use the averaged value tocompute C for each CMUT. The measurements of C at each of the biasvoltages V_(BIAS) may constitute a C vs. V_(BIAS) curve for each CMUT.

If the membrane of a CMUT is stuck to its substrate, the CMUT's C vs.V_(BIAS) curve may not have a discontinuity. This may be because, forthe entire range of V_(BIAS) values, the membrane is collapsed. Thus, insome embodiments, the processing device may determine whether themembrane of a CMUT is stuck to its substrate (referred to for simplicityas a CMUT being “stuck”) by determining whether a discontinuity occursin the C vs. V_(BIAS) curve. The processing device may determine whethera discontinuity occurs by computing the derivative (e.g., first orsecond derivative) of the C vs. V_(BIAS) curve. The processing devicemay then count how many CMUTs are stuck. In some embodiments, if thisnumber exceeds a threshold, the processing device may generate anotification as described with reference to act 4104. In someembodiments, based on this count, the processing device may thendetermine what percentage of the CMUTs from which measurements werecollected are stuck and/or what percentage of the CMUTs in the CMUTarray are stuck. If this percentage exceeds a threshold, the processingdevice may generate a notification as described with reference to act4104. The threshold percentage may be, for example, approximately equalto or between 0.1%-0.5%, 0.1%-1%, 0.1%-5%, 0.1%-10%, 0.1%-15%, 0.1%-20%,0.1%-25%, 0.5%-1%, 0.5%-5%, 0.5%-10%, 0.5%-15%, 0.5%-20%, 0.5%-25%,1-25%, 5-25%, 10-25%, 15-25%, 20-25%, 1-20%, 5-20%, 10-20%, 15-20%,1-15%, 5-15%, 10-15%, 1-10%, or 1-5%. As specific examples, thethreshold percentage may be approximately equal to 1%, 5%, 10%, 15%,20%, or 25%, although other suitable thresholds may be used.

In act 4104, the processing device generates a notification based on thesets of measurements received in act 4102. As described above, theprocessing device may generate the notification if a percentage of stuckCMUTs exceeds a threshold, and the percentage of stuck CMUTs may bedetermined based on the sets of measurement received in act 4102, asdescribed above. The notification may be, for example, that theultrasound device should be replaced. In some embodiments, theprocessing device may generate the notification on its own displayscreen for the user. In some embodiments, the processing device maytransmit, over a wireless network, a notification to a supplier of theultrasound device that the ultrasound device should be replaced.

FIG. 42 illustrates a schematic diagram of a CMUT 4252 (which may be thesame as the CMUT 152), in accordance with certain embodiments describedherein. The CMUT 4252 includes a membrane 4233 and a substrate 4235. Thesubstrate 4235 includes an electrode 4237. In FIG. 42 , the membrane4233 is collapsed onto the substrate 4235, such that the membrane 4233contacts the substrate 4235. The static membrane deflection profile at aDC bias voltage (V_(BIAS)) across the CMUT 4252 is determined by theapplied electrical force and the restoring force of the membrane 4233.Without being limited by theory, the capacitance C of the CMUT 4252 canbe calculated by integrating the ring capacitance of the same deflectiondistance using the following equation:

${{C({VBIAS})} = {\int_{0}^{d}{\frac{2\pi\; ɛ_{0}r}{t_{g - {x{(r)}}}}{dr}}}},$where d is the diameter of the membrane 4233 and t_(g) is the effectiveheight of me gap between the membrane 4233 and the substrate 4235. Itcan be appreciated from the above equation that when there is contactbetween the membrane 4233 and the substrate, meaning that ∃r:t_(g)=x(r), a discontinuity should be observed in the capacitance C vs.V_(BIAS) curve.

FIG. 43 illustrates another schematic diagram of the CMUT 4252 (whichmay be the same as the CMUT 152), in accordance with certain embodimentsdescribed herein. FIG. 43 further illustrates a DC-DC converter 4339 andultrasound circuitry 4341. The DC-DC converter 4339 may be, for example,a charge pump. The DC-DC converter 4339 may be disposed, for example, inan ultrasound device (e.g., the ultrasound device 4402 described below)but not in the substrate 4235. The ultrasound circuitry 4341 is disposedin the substrate 4235 of the CMUT 4252 and is electrically coupled tothe electrode 4237. The ultrasound circuitry 4341 may be, for example,integrated circuitry that is integrated in a semiconductor chip. Theultrasound circuitry 4341 may include, for example, any of theultrasound circuitry, illustrated in FIG. 3-34 or 43 (e.g., theultrasound circuitry 2727, 2827, 2927, 3027, 3127, 3227, 3327, 3427, or4310). The DC-DC converter 4339 may apply a voltage to the membrane 4233of the CMUT and the ultrasound circuitry 4341 may apply a voltage to theelectrode 4237. If the ultrasound circuitry 4341 establishes a virtualground at the electrode 4237, and the DC-DC converter 4339 applies avoltage V_(BIAS) to the membrane 4233, then the voltage applied to theCMUT 4252 (i.e., between the membrane 4233 and the electrode 4237 of theCMUT 152) may be V_(BIAS).

FIG. 44 illustrates a schematic block diagram of an example ultrasoundsystem 4400 upon which various aspects of the technology describedherein may be practiced. The ultrasound system 4400 includes anultrasound device 4402, a processing device 4404, a network 4406, andone or more servers 4408. The processing device 4404 may be any of theprocessing devices described herein. The ultrasound device 4402 may beany of the ultrasound devices described herein.

The ultrasound device 4402 includes ultrasound circuitry 4410. Theprocessing device 4404 includes a camera 4420, a display screen 4412, aprocessor 4414, a memory 4416, an input device 4418, and a speaker 4422.The processing device 4404 is in wired (e.g., through a lightningconnector or a mini-USB connector) and/or wireless communication (e.g.,using BLUETOOTH, ZIGBEE, and/or WiFi wireless protocols) with theultrasound device 4402. The processing device 4404 is in wirelesscommunication with the one or more servers 4408 over the network 4406.

The ultrasound device 4402 may be configured to generate ultrasound datathat may be employed to generate an ultrasound image. The ultrasounddevice 4402 may be constructed in any of a variety of ways. In someembodiments, the ultrasound device 4402 includes a transmitter thattransmits a signal to a transmit beamformer which in turn drivestransducer elements within a transducer array to emit pulsed ultrasonicsignals into a structure, such as a patient. The pulsed ultrasonicsignals may be back-scattered from structures in the body, such as bloodcells or muscular tissue, to produce echoes that return to thetransducer elements. These echoes may then be converted into electricalsignals by the transducer elements and the electrical signals arereceived by a receiver. The electrical signals representing the receivedechoes are sent to a receive beamformer that outputs ultrasound data.The ultrasound circuitry 4410 may be configured to generate theultrasound data. The ultrasound circuitry 4410 may include one or moreultrasonic transducers monolithically integrated onto a singlesemiconductor die. The ultrasonic transducers may include, for example,one or more capacitive micromachined ultrasonic transducers (CMUTs), oneor more CMOS (complementary metal-oxide-semiconductor) ultrasonictransducers (CUTs), one or more piezoelectric micromachined ultrasonictransducers (PMUTs), and/or one or more other suitable ultrasonictransducer cells. In some embodiments, the ultrasonic transducers may beformed on the same chip as other electronic components in the ultrasoundcircuitry 4410 (e.g., transmit circuitry, receive circuitry, controlcircuitry, power management circuitry, and processing circuitry) to forma monolithic ultrasound device. The ultrasound circuitry 4410 mayinclude any of the ultrasound circuitry illustrated in FIGS. 3-34 (e.g.,the ultrasound circuitry 2727, 2827, 2927, 3027, 3127, 3227, 3327, 3427,or 4341) as well as the DC-DC converter 4337. The ultrasound device 4402may transmit ultrasound data and/or ultrasound images to the processingdevice 4404 over a wired (e.g., through a lightning connector or amini-USB connector) and/or wireless (e.g., using BLUETOOTH, ZIGBEE,and/or WiFi wireless protocols) communication link. The ultrasoundcircuitry 4410 may be configured to perform certain of the processesdescribed herein (e.g., the processes 3600, 3700, 3800, and/or 3900).

Referring now to the processing device 4404, the processor 4414 mayinclude specially-programmed and/or special-purpose hardware such as anapplication-specific integrated circuit (ASIC). For example, theprocessor 4414 may include one or more graphics processing units (GPUs)and/or one or more tensor processing units (TPUs). TPUs may be ASICsspecifically designed for machine learning (e.g., deep learning). TheTPUs may be employed to, for example, accelerate the inference phase ofa neural network. The processing device 4404 may be configured toprocess the ultrasound data received from the ultrasound device 4402 togenerate ultrasound images for display on the display screen 4412. Theprocessing may be performed by, for example, the processor 4414. Theprocessor 4414 may also be adapted to control the acquisition ofultrasound data with the ultrasound device 4402. The ultrasound data maybe processed in real-time during a scanning session as the echo signalsare received. In some embodiments, the displayed ultrasound image may beupdated a rate of at least 5 Hz, at least 10 Hz, at least 20 Hz, at arate between 5 and 60 Hz, at a rate of more than 20 Hz. For example,ultrasound data may be acquired even as images are being generated basedon previously acquired data and while a live ultrasound image is beingdisplayed. As additional ultrasound data is acquired, additional framesor images generated from more-recently acquired ultrasound data aresequentially displayed. Additionally, or alternatively, the ultrasounddata may be stored temporarily in a buffer during a scanning session andprocessed in less than real-time.

The processing device 4404 may be configured to perform certain of theprocesses (e.g., the processes 4000-4100) described herein using theprocessor 4414 (e.g., one or more computer hardware processors) and oneor more articles of manufacture that include non-transitorycomputer-readable storage media such as the memory 4416. The processor4414 may control writing data to and reading data from the memory 4416in any suitable manner. To perform certain of the processes describedherein, the processor 4414 may execute one or more processor-executableinstructions stored in one or more non-transitory computer-readablestorage media (e.g., the memory 4416), which may serve as non-transitorycomputer-readable storage media storing processor-executableinstructions for execution by the processor 4414. The camera 4420 may beconfigured to detect light (e.g., visible light) to form an image. Thecamera 4420 may be on the same face of the processing device 4404 as thedisplay screen 4412. The display screen 4412 may be configured todisplay images and/or videos, and may be, for example, a liquid crystaldisplay (LCD), a plasma display, and/or an organic light emitting diode(OLED) display on the processing device 4404. The input device 4418 mayinclude one or more devices capable of receiving input from a user andtransmitting the input to the processor 4414. For example, the inputdevice 4418 may include a keyboard, a mouse, a microphone, touch-enabledsensors on the display screen 4412, and/or a microphone. The displayscreen 4412, the input device 4418, the camera 4420, and the speaker4422 may be communicatively coupled to the processor 4414 and/or underthe control of the processor 4414.

It should be appreciated that the processing device 4404 may beimplemented in any of a variety of ways. For example, the processingdevice 4404 may be implemented as a handheld device such as a mobilesmartphone or a tablet. Thereby, a user of the ultrasound device 4402may be able to operate the ultrasound device 4402 with one hand and holdthe processing device 4404 with another hand. In other examples, theprocessing device 4404 may be implemented as a portable device that isnot a handheld device, such as a laptop. In yet other examples, theprocessing device 4404 may be implemented as a stationary device such asa desktop computer. The processing device 4404 may be connected to thenetwork 4406 over a wired connection (e.g., via an Ethernet cable)and/or a wireless connection (e.g., over a WiFi network). The processingdevice 4404 may thereby communicate with (e.g., transmit data to orreceive data from) the one or more servers 4408 over the network 4406.For example, a party may provide from the server 4408 to the processingdevice 4404 processor-executable instructions for storing in one or morenon-transitory computer-readable storage media (e.g., the memory 4426)which, when executed, may cause the processing device 4404 to performcertain of the processes (e.g., the processes 4000-4100) describedherein. For further description of ultrasound devices and systems, seeU.S. patent application Ser. No. 15/415,434 titled “UNIVERSAL ULTRASOUNDDEVICE AND RELATED APPARATUS AND METHODS,” filed on Jan. 25, 2017 andpublished as U.S. Pat. App. Publication No. 2017-0360397 A1 (andassigned to the assignee of the instant application).

FIG. 44 should be understood to be non-limiting. For example, theultrasound system 4400 may include fewer or more components than shownand the processing device 4404 and ultrasound device 4402 may includefewer or more components than shown. In some embodiments, the processingdevice 4404 may be part of the ultrasound device 4402.

FIG. 45 illustrates an example handheld ultrasound probe 4500, inaccordance with certain embodiments described herein. The handheldultrasound probe 4500 may be the same as the ultrasound device 4402 andmay contain all of the ultrasound circuitry illustrated in FIG. 3-34 or44 (e.g., the ultrasound circuitry 2727, 2827, 2927, 3027, 3127, 3227,3327, 3427, 4341 or 4410).

FIG. 46 illustrates an example wearable ultrasound patch 4600, inaccordance with certain embodiments described herein. The wearableultrasound patch 4600 is coupled to a subject 4602. The wearableultrasound patch 4600 may be the same as the ultrasound device 4402 andmay contain all of the ultrasound circuitry illustrated in FIG. 3-34 or44 (e.g., the ultrasound circuitry 2727, 2827, 2927, 3027, 3127, 3227,3327, 3427, 4341 or 4410).

FIG. 47 illustrates an example ingestible ultrasound pill 4700, inaccordance with certain embodiments described herein. The ingestibleultrasound pill 4700 may be the same as the ultrasound device 4402 andmay contain all of the ultrasound circuitry illustrated in FIG. 3-34 or44 (e.g., the ultrasound circuitry 2727, 2827, 2927, 3027, 3127, 3227,3327, 3427, 4341, or 4410).

Further description of the handheld ultrasound probe 4500, the wearableultrasound patch 4600, and the ingestible ultrasound pill 4700 may befound in U.S. patent application Ser. No. 15/626,711 titled “UNIVERSALULTRASOUND IMAGING DEVICE AND RELATED APPARATUS AND METHODS,” filed onJun. 19, 2017 and published as U.S. Pat. App. Publication No.2017-0360399 A1 (and assigned to the assignee of the instantapplication), which is incorporated by reference herein in its entirety.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

As used herein, reference to a numerical value being between twoendpoints should be understood to encompass the situation in which thenumerical value can assume either of the endpoints. For example, statingthat a characteristic has a value between A and B, or betweenapproximately A and B, should be understood to mean that the indicatedrange is inclusive of the endpoints A and B unless otherwise noted.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, andyet within ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

Having described above several aspects of at least one embodiment, it isto be appreciated various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be object of thisdisclosure. Accordingly, the foregoing description and drawings are byway of example only.

What is claimed is:
 1. An apparatus, comprising: a processing device in operative communication with an ultrasound device, the processing device configured to: receive, from the ultrasound device, sets of measurements of capacitances or a parameter related to the capacitances of one or more CMUTs in the ultrasound device at each of multiple bias voltages applied to membranes of the CMUTs; determine collapse voltages of the one or more CMUTs based on the capacitances of the CMUTs at each of the multiple bias voltages; and cause the ultrasound device to apply a bias voltage to the membranes of the CMUTs based at least in part on the collapse voltages of the one or more CMUTs, wherein each of the measurements of the parameter related to the capacitances of the one or more CMUTs in the ultrasound device comprises a measurement of a time for a ramp voltage to cross a reference voltage, and wherein a current is integrated onto one of the CMUTs to generate the ramp voltage when a particular bias voltage of the multiple bias voltages is applied to the CMUT.
 2. The apparatus of claim 1, wherein the processing device is further configured to compute the capacitances of the one or more CMUTs in the ultrasound device based on the measurements of the parameter related to the capacitances of the one or more CMUTs in the ultrasound device.
 3. The apparatus of claim 1, wherein the processing device is configured, when determining the collapse voltages of the one or more CMUTs based on the capacitances of the one or more CMUTs at each of the multiple bias voltages, to determine a particular bias voltage at which a discontinuity occurs in a curve of capacitance versus bias voltage for each of the one or more CMUTs.
 4. The apparatus of claim 1, wherein the processing device is further configured to average the collapse voltages of the one or more CMUTs to produce an average of the collapse voltages.
 5. The apparatus of claim 4, wherein the processing device is configured, when causing the ultrasound device to apply the bias voltage to the membranes of the one or more CMUTs based at least in part on the collapse voltages of the one or more CMUTs, to cause the ultrasound device to apply a bias voltage to the membranes of the one or more CMUTs that is greater than the average of the collapse voltages by an offset voltage.
 6. The apparatus of claim 5, wherein the membranes of the one or more CMUTs comprise one shared membrane.
 7. The apparatus of claim 5, wherein the offset voltage is approximately equal to or between 25-30V.
 8. The apparatus of claim 5, wherein the processing device is further configured to use different offset voltages when the ultrasound device is imaging different anatomical regions.
 9. A method, comprising: receiving, by a processing device in operative communication with an ultrasound device and from the ultrasound device, sets of measurements of capacitances or a parameter related to the capacitances of one or more CMUTs in the ultrasound device at each of multiple bias voltages applied to membranes of the one or more CMUTs; determining collapse voltages of the one or more CMUTs based on the capacitances of the one or more CMUTs at each of the multiple bias voltages; and causing the ultrasound device to apply a bias voltage to the membranes of the one or more CMUTs based at least in part on the collapse voltages of the one or more CMUTs, wherein each of the measurements of the parameter related to the capacitances of the one or more CMUTs in the ultrasound device comprises a measurement of a time for a ramp voltage to cross a reference voltage, and wherein a current is integrated onto one of the one or more CMUTs to generate the ramp voltage when a particular bias voltage of the multiple bias voltages is applied to the CMUT.
 10. An apparatus, comprising: a processing device in operative communication with an ultrasound device, the processing device configured to: receive, from the ultrasound device, sets of measurements of a capacitance or a parameter related to the capacitance of one or more CMUTs in the ultrasound device at each of multiple bias voltages applied to membranes of the one or more CMUTs; and generate a notification based on the sets of measurements, wherein each of the measurements of the parameter related to the capacitances of the one or more CMUTs in the ultrasound device comprises a measurement of a time for a ramp voltage to cross a reference voltage, and wherein a current is integrated onto one of the CMUTs to generate the ramp voltage when a particular bias voltage of the multiple bias voltages is applied to the CMUT.
 11. The apparatus of claim 10, wherein the processing device is further configured to compute the capacitances of the one or more CMUTs in the ultrasound device based on the measurements of the parameter related to the capacitances of the one or more CMUTs in the ultrasound device.
 12. The apparatus of claim 10, wherein the processing device is further configured to count a number of the CMUTs having a membrane stuck to a substrate.
 13. The apparatus of claim 12, wherein the processing device is configured, when counting the number of the CMUTs having a membrane stuck to a substrate, to count a number of the CMUTs lacking a discontinuity in a curve of capacitance versus bias voltage for each of the one or more CMUTs.
 14. The apparatus of claim 12, wherein the processing device is configured to generate the notification based on the sets of measurements when the number of the CMUTs, a percentage of the CMUTs measured, and/or a percentage of the CMUTs in an array of the ultrasound device have a membrane stuck to the substrate.
 15. The apparatus of claim 10, wherein the notification comprises a notification that the ultrasound device should be replaced.
 16. The apparatus of claim 10, wherein the processing device is configured, when generating the notification, to generate the notification on a display screen of the processing device.
 17. The apparatus of claim 10, wherein the processing device is configured, when generating the notification, to transmit the notification to a supplier of the ultrasound device. 